Limits - Thunderbird: Difference between revisions

From MozillaZine Knowledge Base
Jump to navigationJump to search
(32 intermediate revisions by 3 users not shown)
Line 2: Line 2:


==Accounts==
==Accounts==
 
There is no known limit of the number of accounts you can have. If you run into one, it probably would be either a bug in how many accounts the folder pane can display or due to "Use Global Inbox" being checked for that account. One user is using 150 accounts with Thunderbird 24.0. [http://forums.mozillazine.org/viewtopic.php?f=39&t=2753135]
There is no known limit of the number of accounts you can have. If you run into one, it probably would be either a bug in how many accounts the folder pane can display or due to "Use Global Inbox" being checked for that account. One user mentioned using 90 accounts.


==Address books==
==Address books==
There is no known limit on the number of address books you can have or the number of addresses you can have in a address book though at some point you might want to think about using a LDAP server instead. One user has 30,000 addresses spread across 63 address books. [http://forums.mozillazine.org/viewtopic.php?p=2065149#p2065149]
There is no known limit on the number of address books you can have or the number of addresses in an address book. However, for large numbers of contacts at some point you should consider putting your contacts in an LDAP server instead. (One user has 30,000 addresses spread across 63 address books. [http://forums.mozillazine.org/viewtopic.php?p=2065149#p2065149]. Another has 90,000 addresses in one address book and the address book has become so slow it is unusable. [http://forums.mozillazine.org/viewtopic.php?f=39&t=2865653])


Its not clear what the limits are for the maximum size of a address book or for the notes section in a card.  
Although there might not be limits on the address book size or the notes section in a card, you may easily encounter performance problems when you reach several thousand contacts or have many large notes. The reason is that for every address book that gets used while running Thunderbird, all the contacts in that address book are loaded into memory and stay in memory.  This can result in general slowness of Thunderbird, not just slow address autocomplete. (One user reports a 4,265 KB address book of several contacts, including one with a 4.2MB note. It took a long time to switch to that address book or to switch between one of the normal cards and the one with a 4.2MB note. However, it didn't seem to effect auto-completion when composing a message.)
It appears performance might become too slow for it to be usable before you run into a limit. A 4,265KB address book was created with several cards, including one with a 4.2MB note. It took a long time to swtich to that address book or to switch between one of the normal cards and the one with a 4.2MB note. However, it didn't seem to effect auto-completion when composing a message.


==Attachments==
==Attachments==
Line 18: Line 16:
==Cookies==
==Cookies==
Thunderbird [[RSS_cookies_(Thunderbird) | disables cookies by default]], but they can be useful for RSS and the Webmail and ThunderBrowse extensions. You can copy and reuse the cookies.txt file from your Firefox profile. Firefox defaults to a limit of 50 cookies per site and 1000 total, which you can change using network.cookie.maxPerHost and network.cookie.maxNumber . Since Thunderbird doesn't support those preferences the limit appears to be the default value in Firefox.
Thunderbird [[RSS_cookies_(Thunderbird) | disables cookies by default]], but they can be useful for RSS and the Webmail and ThunderBrowse extensions. You can copy and reuse the cookies.txt file from your Firefox profile. Firefox defaults to a limit of 50 cookies per site and 1000 total, which you can change using network.cookie.maxPerHost and network.cookie.maxNumber . Since Thunderbird doesn't support those preferences the limit appears to be the default value in Firefox.
==Custom headers==
There is a limit of 50 [[Custom_headers | custom headers]] (they are defined using the "customize..." option at the bottom of the leftmost list box in searches and message filters, or by editing mailnews.customHeaders using the config editor) .  [https://mxr.mozilla.org/comm-central/source/mail/locales/en-US/chrome/messenger/filter.properties]


==E-mail addresses==
==E-mail addresses==
Line 24: Line 25:
You can receive messages sent to multiple addresses in the same mailbox. Any limitations would be due to your e-mail provider.  
You can receive messages sent to multiple addresses in the same mailbox. Any limitations would be due to your e-mail provider.  


==File descriptors==
==Open files==
A file descriptor is a data structure used to access a file, normally only used with [http://en.wikipedia.org/wiki/POSIX POSIX] operating systems. [http://forums.mozillazine.org/viewtopic.php?t=544126 Supposedly] there is a hard coded limit in Thunderbird of 256 file descriptors under Solaris. If you open 256 different folders you'll run into that limit, even if you closed most of the folders. Nobody has mentioned a similar problem on other operating systems.
A file descriptor/file handle is a data structure used to access a file via operating system functions. [http://forums.mozillazine.org/viewtopic.php?t=544126 Supposedly] there is a hard coded limit in Thunderbird of 256 file descriptors under Solaris. On Linux, the OS limit of open files is around 1024 by default. For folders backed by mbox storage, opening a folder means opening the file containing the message data. If you open too many different folders you'll run into that limit, even if you closed most of the folders (there is a cache keeping old folders open for a while). Once the limit is reached, this may cause a "Unable to load address book" or a "Unable to open summary file error" messages. [http://forums.mozillazine.org/viewtopic.php?f=39&t=3026471][https://bugzilla.mozilla.org/show_bug.cgi?id=495911]


==Folders and messages==
==Folders and messages==
The number of messages in a folder is limited to 4 billion (2^32 in a 32bit counter)[https://bugzilla.mozilla.org/show_bug.cgi?id=1261357#c5].


Outlook 2002 (and earlier versions) has a 2GB limit for the maximum size of a .PST file. It stores all of the folders in a central file. Outlook Express stores each folder in a separate .DBX file, which has a 2GB maximum size. Windows Live Mail stores each message in a separate file (*.EML for mail and *.NWS for news posts). Thunderbird (like Eudora, Mulberry, SeaMonkey and PocoMail) stores each folder in a separate text file, using the mbox format. Offline folders use mbox files too.
The maximum size of a single message is currently also limited to 4GB.


There is no known limit on the number of folders. The maximum size of a folder used to be 4GB unless the file system limited the maximum file size or you ran into a bug where Thunderbird limited it to 2GB due to using a 32 signed integer when manipulating the file. Its not clear why 4GB was chosen as the limit, though that is the maximum file size in FAT32. Thunderbird 3.1 added a 64-bit offset to the .msf file allowing folders larger than 4GB (if the file system permits that large a file). However, using folders greater than 4GB is not recommended as compacting will take a long time.  [http://forums.mozillazine.org/viewtopic.php?p=11291447#p11291447] [https://bugzilla.mozilla.org/show_bug.cgi?id=532323]
Folder space/size limits depend on whether you are using mbox or maildir storage format. Messages are stored by default as [http://en.wikipedia.org/wiki/Mbox mbox] where messages of a folder are stored in one file. A folder needs to be periodically [[Compacting_folders | compacted]] to remove deleted messages and reduce the size of the folder file.


The mbox files (your folders) are stored in a [[profile folder]] on your boot disk by default. This would normally limit how much mail you can store to the free space on your boot disk. However, you can use the [[Profile Manager]] to create a profile wherever you want (including file shares). It's also possible to configure the mail directories and/or the Local Folders directory to be [[Moving your mail storage location (Thunderbird)| stored outside of the profile]], on any drive or directory. This means the effective limit is how much free disk space you have.
You are also limited by the amount of free space available on the disk where your mail files are stored.  By default the files are stored in a [[profile folder | Thunderbird profile]] on your PC. They can be somewhere else if you have moved the location of your OS's "user data", used the [[Profile Manager]] to put the profile elsewhere, or [[Moving your mail storage location (Thunderbird)| stored mail folders outside of the Thunderbird profile]] - which can even be a file share on a different computer.


Thunderbird 3.1 added support for a "[https://wiki.mozilla.org/Thunderbird:Pluggable_Mail_Stores pluggable mail store]". Its being tested to verify it would work using maildir or SQLite files, but there aren't any prototypes for those implementations yet.
Prior to version 3.1, the maximum folder size is 4GB or as limited by your file system. This is the same as the maximum file size under FAT32. NTFS (Windows), ext3, ext4 and ReiserFS (Linux), and HFS Plus (OS X) support much larger file sizes, and a "All Mail" folder in a Gmail IMAP account is contains a copy of all messages in the mailbox (which could exceed 10GB) so eventually the limits were changed.  Thunderbird 3.1 added a a 64-bit offset to the .msf file allowing '''imap''' folders larger than 4GB, if the file system permitted large files [http://forums.mozillazine.org/viewtopic.php?p=11291447#p11291447] [https://bugzilla.mozilla.org/show_bug.cgi?id=532323]. This change did not help non-imap folders, for example those in Local Folders, including any offline storage (Tools -> Account Settings -> Synchronization & Storage ->Message Synchronizing) for remote folders. Offline storage uses mbox files, just like POP accounts and the Local Folders pseudo account.


If you use a desktop search program such as Google Desktop , Copernic or X1 it may not be able to index the contents of a 4GB folder. X1 supposedly runs into problems at 1GB.
The 4GB limit was finally removed starting with Thunderbird 51. Folders are allowed to grow beyond 4GB by default on current systems. [https://bugzilla.mozilla.org/show_bug.cgi?id=789679]


When copying and pasting text from a word processor into a Thunderbird composition window, one user reported a limit of 908KB of text. Text beyond that limit did not appear when the text was pasted into Thunderbird.
On filesystems that do not support files larger than 4GB (e.g. FAT32) or for performance reasons
you may wish to set the preference mailnews.allowMboxOver4GB to false so
that TB knows to not cross the 4GB limit per folder. At an attempt of that, it will responds with a "folder is full" error message.
 
(Not finished/Not recommended for use) Thunderbird 12 added a pluggable storage API which the maildir storage format (and the current Berkeley mbox). Maildir stores each message as an individual files, i.e. does not combine messages into a single file, and thus bypasses the 4GB folder size as well as eliminates any need to compact a folder. The maildir support, also called maildir-lite in Thunderbird, is very similar to, but not meant to be 100% compatible with, the maildir spec. It was hoped that maildir would be enabled by default in Thunderbird 24.0 (Fall 2013) but it is still too buggy for normal use. [https://bugzilla.mozilla.org/show_bug.cgi?id=58308] [https://bugzilla.mozilla.org/show_bug.cgi?id=845952]. Maildir also needs a rebuild index mechanism since power uses may fiddle with the contents of the maildir folder from the command line or a file manager. But the maildir support is improving. With Thunderbird 52 it is now possible to choose using maildir via the account manager UI when creating a new account.


===Bugs===
===Bugs===
There are bug reports about some versions (mainly for OSX and some BSD systems) that accidentally lowered the maximum folder size to 2GB and some scenarios where Thunderbird doesn't check that adding a message will exceed the maximum folder size before it adds it.
The support for folders larger than 4GB appears to be broken in recent versions (such as 16.0.2). [https://bugzilla.mozilla.org/show_bug.cgi?id=789679]. There has been a lot of confusion over how wide spread the problem is, and there are no tests for it in the [https://moztrap.mozilla.org/manage/cases/ Moztrap] test case management software (it replaced [https://litmus.mozilla.org/ Litmus], which didn't test it either). There has also been confusion due to a bug (now fixed) that caused repeated downloading of messages for a offline folder in a IMAP account due to changes in how Thunderbird determined the real message size. [https://bugzilla.mozilla.org/show_bug.cgi?id=806760]


Normally whether or not a folder is [[Compacting_folders | corrupted]] has no effect on the maximum size of the mbox file. However, in a very few cases the corruption caused Thunderbird to ignore the maximum file size, once reaching [http://forums.mozillazine.org/viewtopic.php?f=39&t=1239485 35GB] .
There are old bug reports for some versions before 12.0  (mainly for OSX and some BSD systems) were the maximum folder size was accidentally lowered to 2GB. There were also some scenarios where Thunderbird didn't check that adding a message would exceed the maximum folder size before it added it. Normally whether or not a folder is [[Compacting_folders | corrupted]] has no effect on the maximum size of the mbox file. However, in a very few cases the corruption caused Thunderbird to ignore the maximum folder size, once reaching [http://forums.mozillazine.org/viewtopic.php?f=39&t=1239485 35GB] .
 
Most of these problems should be fixed with Thunderbird 52.
 
There is a known problem that for maildir backed folders, the size of
a non-empty folder in the Thunderbird interface is reported as 0 or some other
low value. This does not mean the folder was corrupted or messages are
lost. It just means maildir does not yet report its size properly. [https://bugzilla.mozilla.org/show_bug.cgi?id=1032360]
 
Compacting a folder larger than 4GB may be a bit slow on slower disks or network shares.
 
Desktop search programs such as Google Desktop, Copernic or X1 may not be able to index the contents of a 4GB folder. X1 supposedly runs into problems at 1GB.


==Folder hierarchies==
==Folder hierarchies==
The depth of the folder hierarchy is limited by the string length of the path to last folder's header. That can't exceed the operating system's maximum path length (usually at least 255 characters). But the OS length is not the same as what you see in the Thunderbird folder pane. The OS length includes the path to the parent folder in the profile (which might be over 100 characters), and five additional characters (back slash plus .sbd) for each child folder. If you hit this limit you can display more folders by moving the profile or the accounts directory closer to the root directory of the drive, so that less of the total path length is wasted. There is additional overhead if any of the folders have non-ASCII characters. For example, if it is an IMAP account the server would send the string as modified UTF-7, which more than doubles the number of characters.
[https://bugzilla.mozilla.org/show_bug.cgi?id=249807 Bug 249807] prevents Thunderbird from displaying a child folder if the total length of the child folder's relative path exceeds 128 bytes. The relative path is the distance from the top (root) of the profile directory (not the total path length).
With local folders (POP accounts) you normally can't create a folder hierarchy that you can't fully use.  However, that's not true for IMAP accounts since you can create it using webmail, and then not be able to download all of the headers due to it exceeding the maximum path length. This limit doesn't apply to a Subscribe window in a IMAP account since it just lists what folders exist on the mail server (it is not downloading headers).


The depth of the folder hierarchy is limited by the path to last folders header. That can't exceed the operating systems maximum path length (normally 255 characters). That is not the same as what you see in the folder pane, its includes the path to the parent folder in the profile (which might be over 100 characters), and five additional characters (back slash plus .sbd) for each child folder. If you run into this limit you can display more folders by moving the profile or the accounts directory closer to the root of the drive, so that less of the total path length is wasted. There is additional overhead if any of the folders have non-ASCII characters. For example, if its a IMAP account the server would send the string as modified UTF-7, which more than doubles the number of characters.
The number of folders in a IMAP account might be limited by the IMAP server. For example, Gmail supposedly imposes a limit of 5000 labels/sub-labels. Each label is represented as a folder by the IMAP server. [https://www.howtogeek.com/school/gmail-guide/lesson3/]


With local folders (POP accounts) you normally can't create a folder hierarchy that you can't fully use.  However, thats not true for IMAP accounts since you could create it using webmail, and not be able to download all of the headers due to it exceeding the maximum path length. This limit doesn't apply to a Subscribe window in a IMAP account since it just lists what folders exist on the mail server (its not downloading headers).
==Junk==
The maximum number of tokens used by the junk mail controls defaults to 300,000. That is set in mailnews.bayesian_spam_filter.junk_maxtokens. "When the number of stored anti-junk tokens hits a predefined limit, then tokens are pruned in such a way that effectively reduces the influence of old tokens by 1/2 relative to new tokens, and eliminates rarely used tokens." [https://groups.google.com/forum/#!topic/mozilla.support.thunderbird/hpg8ZaRI6yQ]


==Message Pane==
==Message Pane==
If you use View -> Sort by -> Threaded and select more than 100 messages it will not list more than 100 conversations in the message pane. If you reach that limit you should see something like ''These messages take up: 14.4 MB. (Note: 287 messages are selected, the first 100 are shown)'' if you scroll to the bottom of the message pane.
If you use View -> Sort by -> Threaded and select more than 500 messages it will not list more than 500 conversations in the message pane. If you reach that limit you should see something like ''These messages take up: 14.4 MB. (Note: 1287 messages are selected, the first 500 are shown)'' if you scroll to the bottom of the message pane.


==Message filters and custom headers==
==Message filters==
The Mozilla  [http://www.mozilla.org/mailnews/specs/filters/ message filter specification] states you can create any number of custom headers and message filters. It doesn't state how many rules you can have. However, one of the
There is no known limit to the number of [[Message_Filters | message filters]]. It has been tested that even 10,000 filters can be managed properly in the Filter list dialog. However, message filters have a limit of 50 custom headers.
[http://mxr.mozilla.org/thunderbird/source/mail/locales/en-US/chrome/messenger/filter.properties source files] has several error messages about a limit of 50 custom headers which one [http://forums.mozillazine.org/viewtopic.php?f=39&t=879395&p=4612665 user] has run into.  


==Multiple Identities==
==Multiple Identities==
There is no known limit on the number of [[Multiple_identities_per_e-mail_account | multiple identities]] (additional identities, not created due to creating an account). One user has 60. [http://forums.mozillazine.org/viewtopic.php?p=11725235#p11725235]
There is no known limit on the number of [[Multiple_identities_per_e-mail_account | multiple identities]] (additional identities, not created due to creating an account). One user has 60. [http://forums.mozillazine.org/viewtopic.php?p=11725235#p11725235]
==Number of recent folders==
The list of recent folders when moving a message via Message -> Move To -> Recent is hard coded to a maximum of 15. The same limit is used for Message -> Copy To -> Recent. [http://forums.mozillazine.org/viewtopic.php?f=28&t=2710625]
==Number of connections==
The advanced server settings for a IMAP account specify the maximum number of server connections to cache. It appears to impose a limit of 1000. However most email providers impose a limit for the maximum number of connections from a specific IP address, and the maximum number of connections to a account/mailbox regardless of what devices are used. For example, Gmail imposes a limit of 15 connections per account [https://apple.stackexchange.com/questions/97569/mail-app-keeps-asking-for-google-password] .
If you have several PC's making a connection to the Internet through a router that supports [https://en.wikipedia.org/wiki/Network_address_translation NAT] they might all use the same TCP-IP address. Courier IMAP servers default to 4 connections per TCP-IP address. See [[IMAP:_advanced_account_configuration]] for more information.
==Open .msf files==
Thunderbird loads the contents of the corresponding *.msf file into memory whenever it opens a folder. Starting with Thunderbird 15 there are default settings (mail.db.idle_limit and mail.db.max_open) to limit how many of those files it will keep open, and for how long. This can have a big effect on memory usage if you have tens of thousands of messages in a folder. Its not clear if there is any limit on how many of these files can be open at the same time. One user had 226 *.msf files open. [http://forums.mozillazine.org/viewtopic.php?f=39&t=2459825&p=11943887#p11943887]
However, the number of open folders is limited by the operating system via the number of allowed file
descriptors (see the section above). If you get a error message like "''Unable to load address book file abook.mab. It may be read-only, or locked by another application. Please try again later.''" and you are running a 32-bit version of Windows you might have run into a limit on the number of open file handles that the operating system supports, caused by having lots of mail folders. Thunderbird opens the *.msf file for every mail folder. [https://bugzilla.mozilla.org/show_bug.cgi?id=495911] [http://blogs.technet.com/b/markrussinovich/archive/2009/09/29/3283844.aspx]
==Search results==
Global search limits search results to 400 hits, and requires a minimum of 3 characters in the search string for performance reasons. [https://bugzilla.mozilla.org/show_bug.cgi?id=537856] [https://bugzilla.mozilla.org/show_bug.cgi?id=742236] [http://forums.mozillazine.org/viewtopic.php?p=12022787#p12022787]  [http://forums.mozillazine.org/viewtopic.php?f=31&t=3005591]
Quick search (Ctrl+Shift+F) and the Quick Filter bar don't appear to have any limits. Any limits for "Search the web" (OpenSearch) would be imposed by the search provider.


==SMTP Servers==
==SMTP Servers==
There is no known limit on the number of SMTP servers you can have. Unlike accounts, Thunderbird doesn't appear to test whether the additional SMTP server would be a duplicate.
There is no known limit on the number of SMTP servers you can have. Unlike accounts, Thunderbird doesn't appear to test whether the additional SMTP server would be a duplicate.
==Temporary Files==
Thunderbird is limited to 10,000 [[Nstmp_folders | nstmp]] temporary files . If Thunderbird is interrupted during the compacting, it will abort, and the temporary file will not be deleted. [https://bugzilla.mozilla.org/show_bug.cgi?id=673703]
==Windows and tabs==
The limits on the number of windows and tabs are not clear. There are what appear to be limits of eight compose message windows, ten content tabs, and ten web search tabs. However, you can create several dozen compose message windows. The limit of eight compose message windows occurs if you select several messages and then press Ctrl+R to reply to them. [http://mxr.mozilla.org/comm-central/source/mail/base/content/mailCommands.js#233][http://forums.mozillazine.org/viewtopic.php?f=39&t=2457377] [http://mxr.mozilla.org/comm-central/source/mail/base/content/specialTabs.js#564]  [http://mxr.mozilla.org/comm-central/source/mail/base/content/webSearchTab.js#65]


==Limitations of Microsoft Windows==
==Limitations of Microsoft Windows==
In some cases, Windows users may run into a hard limit placed on the maximum amount of characters any path can be. Symptoms may include, but aren't limited to, disappearing mail folders.
In some cases, Windows users may run into a hard limit placed on the maximum amount of characters any path can be. Symptoms may include, but aren't limited to, disappearing mail folders. The limit is usually a length of 260 characters unless an application supports UNICODE paths. Thunderbird doesn't appear to support UNICODE paths. [http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247%28v=vs.85%29.aspx]


For more information on this, see this Microsoft Knowledge Base article regarding [http://support.microsoft.com/kb/177665/EN-US/ MAX_PATH].
==General remarks==
Also, see the following [http://forums.mozillazine.org/viewtopic.php?t=263489&highlight=&sid=14b3e805e0fdb9dc4364348958e38e6f discussion] on MozillaZine forums.
In all the sections above the phrase "no known limit" means there is no
practical limit on the number of objects. Technically, there is usually an
internal limit of 2 or 4 billion (2^31 or 2^32) due to the
C++ representation of a counter or an index into the list of the objects. But users will run into
issues (performance and/or display) much sooner before approaching this architectural
limit.


==See also==
==See also==
Line 81: Line 133:
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=402392 supporting other message storage formats]
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=402392 supporting other message storage formats]
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=58308 supporting maildir format]
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=58308 supporting maildir format]
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=1078367 allow maildir backed mail folders to exceed 4GB in size] (easier to get them to support > 4GB since they don't use 32bit file offsets like mbox does).
* Bug report about [https://bugzilla.mozilla.org/show_bug.cgi?id=789679 allowing folders larger than 4GB]
* [https://wiki.mozilla.org/Thunderbird:Pluggable_Mail_Stores Pluggable mail stores wiki page]
* [https://wiki.mozilla.org/Thunderbird:Pluggable_Mail_Stores Pluggable mail stores wiki page]
* [http://en.wikipedia.org/wiki/Comparison_of_file_systems Comparison of file systems]
* [http://en.wikipedia.org/wiki/Comparison_of_file_systems Comparison of file systems]

Revision as of 21:50, 22 May 2017

This article describes the known limits. However, there is always the possibility of a configuration specific bug or a bug fix for a lower limit breaking in a maintenance release.

Accounts

There is no known limit of the number of accounts you can have. If you run into one, it probably would be either a bug in how many accounts the folder pane can display or due to "Use Global Inbox" being checked for that account. One user is using 150 accounts with Thunderbird 24.0. [1]

Address books

There is no known limit on the number of address books you can have or the number of addresses in an address book. However, for large numbers of contacts at some point you should consider putting your contacts in an LDAP server instead. (One user has 30,000 addresses spread across 63 address books. [2]. Another has 90,000 addresses in one address book and the address book has become so slow it is unusable. [3])

Although there might not be limits on the address book size or the notes section in a card, you may easily encounter performance problems when you reach several thousand contacts or have many large notes. The reason is that for every address book that gets used while running Thunderbird, all the contacts in that address book are loaded into memory and stay in memory. This can result in general slowness of Thunderbird, not just slow address autocomplete. (One user reports a 4,265 KB address book of several contacts, including one with a 4.2MB note. It took a long time to switch to that address book or to switch between one of the normal cards and the one with a 4.2MB note. However, it didn't seem to effect auto-completion when composing a message.)

Attachments

Thunderbird doesn't appear to impose any limit on the number of attachments or the maximum size of the attachment you can send in a message. Any limits are due to your e-mail provider or SMTP server. Note that sending a binary file as a attachment increases its size by a third due to base64 encoding sending two 8-bit characters as three 7-bit ASCII characters.

Thunderbird 1.5 is incompatible with Outlook in how it stores the filenames of attachments when they exceed 64 bytes. This article provides more information and a workaround.

Cookies

Thunderbird disables cookies by default, but they can be useful for RSS and the Webmail and ThunderBrowse extensions. You can copy and reuse the cookies.txt file from your Firefox profile. Firefox defaults to a limit of 50 cookies per site and 1000 total, which you can change using network.cookie.maxPerHost and network.cookie.maxNumber . Since Thunderbird doesn't support those preferences the limit appears to be the default value in Firefox.

Custom headers

There is a limit of 50 custom headers (they are defined using the "customize..." option at the bottom of the leftmost list box in searches and message filters, or by editing mailnews.customHeaders using the config editor) . [4]

E-mail addresses

There appears to be a limit of approximately 60 addresses when sending messages if you enter each address separately. However, if you use lists (mail distribution lists) for most of the addresses any limit is imposed by whatever SMTP server you use.

You can receive messages sent to multiple addresses in the same mailbox. Any limitations would be due to your e-mail provider.

Open files

A file descriptor/file handle is a data structure used to access a file via operating system functions. Supposedly there is a hard coded limit in Thunderbird of 256 file descriptors under Solaris. On Linux, the OS limit of open files is around 1024 by default. For folders backed by mbox storage, opening a folder means opening the file containing the message data. If you open too many different folders you'll run into that limit, even if you closed most of the folders (there is a cache keeping old folders open for a while). Once the limit is reached, this may cause a "Unable to load address book" or a "Unable to open summary file error" messages. [5][6]

Folders and messages

The number of messages in a folder is limited to 4 billion (2^32 in a 32bit counter)[7].

The maximum size of a single message is currently also limited to 4GB.

Folder space/size limits depend on whether you are using mbox or maildir storage format. Messages are stored by default as mbox where messages of a folder are stored in one file. A folder needs to be periodically compacted to remove deleted messages and reduce the size of the folder file.

You are also limited by the amount of free space available on the disk where your mail files are stored. By default the files are stored in a Thunderbird profile on your PC. They can be somewhere else if you have moved the location of your OS's "user data", used the Profile Manager to put the profile elsewhere, or stored mail folders outside of the Thunderbird profile - which can even be a file share on a different computer.

Prior to version 3.1, the maximum folder size is 4GB or as limited by your file system. This is the same as the maximum file size under FAT32. NTFS (Windows), ext3, ext4 and ReiserFS (Linux), and HFS Plus (OS X) support much larger file sizes, and a "All Mail" folder in a Gmail IMAP account is contains a copy of all messages in the mailbox (which could exceed 10GB) so eventually the limits were changed. Thunderbird 3.1 added a a 64-bit offset to the .msf file allowing imap folders larger than 4GB, if the file system permitted large files [8] [9]. This change did not help non-imap folders, for example those in Local Folders, including any offline storage (Tools -> Account Settings -> Synchronization & Storage ->Message Synchronizing) for remote folders. Offline storage uses mbox files, just like POP accounts and the Local Folders pseudo account.

The 4GB limit was finally removed starting with Thunderbird 51. Folders are allowed to grow beyond 4GB by default on current systems. [10]

On filesystems that do not support files larger than 4GB (e.g. FAT32) or for performance reasons you may wish to set the preference mailnews.allowMboxOver4GB to false so that TB knows to not cross the 4GB limit per folder. At an attempt of that, it will responds with a "folder is full" error message.

(Not finished/Not recommended for use) Thunderbird 12 added a pluggable storage API which the maildir storage format (and the current Berkeley mbox). Maildir stores each message as an individual files, i.e. does not combine messages into a single file, and thus bypasses the 4GB folder size as well as eliminates any need to compact a folder. The maildir support, also called maildir-lite in Thunderbird, is very similar to, but not meant to be 100% compatible with, the maildir spec. It was hoped that maildir would be enabled by default in Thunderbird 24.0 (Fall 2013) but it is still too buggy for normal use. [11] [12]. Maildir also needs a rebuild index mechanism since power uses may fiddle with the contents of the maildir folder from the command line or a file manager. But the maildir support is improving. With Thunderbird 52 it is now possible to choose using maildir via the account manager UI when creating a new account.

Bugs

The support for folders larger than 4GB appears to be broken in recent versions (such as 16.0.2). [13]. There has been a lot of confusion over how wide spread the problem is, and there are no tests for it in the Moztrap test case management software (it replaced Litmus, which didn't test it either). There has also been confusion due to a bug (now fixed) that caused repeated downloading of messages for a offline folder in a IMAP account due to changes in how Thunderbird determined the real message size. [14]

There are old bug reports for some versions before 12.0 (mainly for OSX and some BSD systems) were the maximum folder size was accidentally lowered to 2GB. There were also some scenarios where Thunderbird didn't check that adding a message would exceed the maximum folder size before it added it. Normally whether or not a folder is corrupted has no effect on the maximum size of the mbox file. However, in a very few cases the corruption caused Thunderbird to ignore the maximum folder size, once reaching 35GB .

Most of these problems should be fixed with Thunderbird 52.

There is a known problem that for maildir backed folders, the size of a non-empty folder in the Thunderbird interface is reported as 0 or some other low value. This does not mean the folder was corrupted or messages are lost. It just means maildir does not yet report its size properly. [15]

Compacting a folder larger than 4GB may be a bit slow on slower disks or network shares.

Desktop search programs such as Google Desktop, Copernic or X1 may not be able to index the contents of a 4GB folder. X1 supposedly runs into problems at 1GB.

Folder hierarchies

The depth of the folder hierarchy is limited by the string length of the path to last folder's header. That can't exceed the operating system's maximum path length (usually at least 255 characters). But the OS length is not the same as what you see in the Thunderbird folder pane. The OS length includes the path to the parent folder in the profile (which might be over 100 characters), and five additional characters (back slash plus .sbd) for each child folder. If you hit this limit you can display more folders by moving the profile or the accounts directory closer to the root directory of the drive, so that less of the total path length is wasted. There is additional overhead if any of the folders have non-ASCII characters. For example, if it is an IMAP account the server would send the string as modified UTF-7, which more than doubles the number of characters.

Bug 249807 prevents Thunderbird from displaying a child folder if the total length of the child folder's relative path exceeds 128 bytes. The relative path is the distance from the top (root) of the profile directory (not the total path length).

With local folders (POP accounts) you normally can't create a folder hierarchy that you can't fully use. However, that's not true for IMAP accounts since you can create it using webmail, and then not be able to download all of the headers due to it exceeding the maximum path length. This limit doesn't apply to a Subscribe window in a IMAP account since it just lists what folders exist on the mail server (it is not downloading headers).

The number of folders in a IMAP account might be limited by the IMAP server. For example, Gmail supposedly imposes a limit of 5000 labels/sub-labels. Each label is represented as a folder by the IMAP server. [16]

Junk

The maximum number of tokens used by the junk mail controls defaults to 300,000. That is set in mailnews.bayesian_spam_filter.junk_maxtokens. "When the number of stored anti-junk tokens hits a predefined limit, then tokens are pruned in such a way that effectively reduces the influence of old tokens by 1/2 relative to new tokens, and eliminates rarely used tokens." [17]

Message Pane

If you use View -> Sort by -> Threaded and select more than 500 messages it will not list more than 500 conversations in the message pane. If you reach that limit you should see something like These messages take up: 14.4 MB. (Note: 1287 messages are selected, the first 500 are shown) if you scroll to the bottom of the message pane.

Message filters

There is no known limit to the number of message filters. It has been tested that even 10,000 filters can be managed properly in the Filter list dialog. However, message filters have a limit of 50 custom headers.

Multiple Identities

There is no known limit on the number of multiple identities (additional identities, not created due to creating an account). One user has 60. [18]

Number of recent folders

The list of recent folders when moving a message via Message -> Move To -> Recent is hard coded to a maximum of 15. The same limit is used for Message -> Copy To -> Recent. [19]

Number of connections

The advanced server settings for a IMAP account specify the maximum number of server connections to cache. It appears to impose a limit of 1000. However most email providers impose a limit for the maximum number of connections from a specific IP address, and the maximum number of connections to a account/mailbox regardless of what devices are used. For example, Gmail imposes a limit of 15 connections per account [20] .

If you have several PC's making a connection to the Internet through a router that supports NAT they might all use the same TCP-IP address. Courier IMAP servers default to 4 connections per TCP-IP address. See IMAP:_advanced_account_configuration for more information.

Open .msf files

Thunderbird loads the contents of the corresponding *.msf file into memory whenever it opens a folder. Starting with Thunderbird 15 there are default settings (mail.db.idle_limit and mail.db.max_open) to limit how many of those files it will keep open, and for how long. This can have a big effect on memory usage if you have tens of thousands of messages in a folder. Its not clear if there is any limit on how many of these files can be open at the same time. One user had 226 *.msf files open. [21]

However, the number of open folders is limited by the operating system via the number of allowed file descriptors (see the section above). If you get a error message like "Unable to load address book file abook.mab. It may be read-only, or locked by another application. Please try again later." and you are running a 32-bit version of Windows you might have run into a limit on the number of open file handles that the operating system supports, caused by having lots of mail folders. Thunderbird opens the *.msf file for every mail folder. [22] [23]

Search results

Global search limits search results to 400 hits, and requires a minimum of 3 characters in the search string for performance reasons. [24] [25] [26] [27]

Quick search (Ctrl+Shift+F) and the Quick Filter bar don't appear to have any limits. Any limits for "Search the web" (OpenSearch) would be imposed by the search provider.

SMTP Servers

There is no known limit on the number of SMTP servers you can have. Unlike accounts, Thunderbird doesn't appear to test whether the additional SMTP server would be a duplicate.

Temporary Files

Thunderbird is limited to 10,000 nstmp temporary files . If Thunderbird is interrupted during the compacting, it will abort, and the temporary file will not be deleted. [28]

Windows and tabs

The limits on the number of windows and tabs are not clear. There are what appear to be limits of eight compose message windows, ten content tabs, and ten web search tabs. However, you can create several dozen compose message windows. The limit of eight compose message windows occurs if you select several messages and then press Ctrl+R to reply to them. [29][30] [31] [32]

Limitations of Microsoft Windows

In some cases, Windows users may run into a hard limit placed on the maximum amount of characters any path can be. Symptoms may include, but aren't limited to, disappearing mail folders. The limit is usually a length of 260 characters unless an application supports UNICODE paths. Thunderbird doesn't appear to support UNICODE paths. [33]

General remarks

In all the sections above the phrase "no known limit" means there is no practical limit on the number of objects. Technically, there is usually an internal limit of 2 or 4 billion (2^31 or 2^32) due to the C++ representation of a counter or an index into the list of the objects. But users will run into issues (performance and/or display) much sooner before approaching this architectural limit.

See also

External links