From MozillaZine Knowledge Base

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 mentioned using 90 accounts.

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.

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.

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.

File descriptors

A file descriptor is a data structure used to access a file, normally only used with POSIX operating systems. 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.

Folders and messages

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 seperate .DBX file, which has a 2GB maximum size. Thunderbird stores each folder in a separate text file, using the mbox format.

There is no known limit on the number of folders. The maximum size of a folder is 4GB unless the file system limits the maximum file size to a lower value. This shouldn't be an issue unless you're using OS/2. 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 stored outside of the profile, on any drive or directory. This means the effective limit is how much free disk space you have.

One user had a 4,195,013 KB folder before they got a error message that the folder was full. If you use the Gigabyte definition commonly used for memory and file sizes (rather than the one used for hard drive capacity) it was about 1MB larger than the quoted limit. 4 * 1,073,741,824 bytes = 4,294,967,296 bytes * (1KB/1024 bytes) = 4,194,304 KB.

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.

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.

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.

For more information on this, see this Microsoft Knowledge Base article regarding MAX_PATH. Also, see the following discussion on MozillaZine forums.

See also

• Multiple identities per e-mail account

External links

• Comparison of file systems
• Multiple Accounts API
• Maximum size of a .PST file
• Maximum size of a .DBX file
• PST2GB A tool used to reduce the size of a .pst file if its over 2GB. You may need to use it to recover the data before trying to import it into Thunderbird.