Common misconceptions about Thunderbird
From MozillaZine Knowledge Base
A lot of users have mistaken ideas about what Thunderbird is or how it works that cause problems when they try to use it. This article tries to clear up some of the most common misconceptions. It assumes you are using Thunderbird 3.1 or later under Windows though it is still useful if you're using an earlier version or a different operating system.
Thunderbird will assign you an email address
Thunderbird is just an email client, not an email provider. Your email provider provides the mail server(s) that get, store and send messages, and assigns you a email address. Thunderbird sends the mail server commands using standard POP3, IMAP and SMTP protocols after remotely logging in to your account on that mail server. While Thunderbird provides a lot of extra functionality, it's basically just a convenient alternative to logging into webmail using a browser.
Most users already have an account (and email address) provided by a email provider such as your ISP, university, AOL, Google (Gmail), GMX, Yahoo, Microsoft (MSN) etc. and don't want to change it or lose the option of using webmail. When you create an "account" in Thunderbird you're basically just telling it how to connect to the mail server and use your existing mail account (and email address). The Thunderbird account wizard automates most of that, you normally just have to tell it your name, email address, and password.
Get an account is an experimental add-on that lets you create an account from scratch, which eventually will be built into Thunderbird. If you use this add-on you're paying both for an account provided by a reseller (Tucows/Hover), and for the convenience of not having to sign up for the account beforehand. You're also buying a pig in the poke since so little information is provided about your account (not even who the actual email provider is). Its not recommended.
If your add-on isn't supported you need to wait for a version of Thunderbird that supports it
Frequently you can install and use an add-on that doesn't formally support your version of Thunderbird if you disable the version checking, or edit the add-on to "bump" the version limit. It depends upon what API's it uses whether it works. Counter-intuitively, the older an add-on the less likely there is a problem. If it doesn't work it's extremely rare for it to do any harm, just uninstall it.
Version checking was intended as a way to minimize problems by making certain that users only used add-ons that were meant to be used with their version of Thunderbird. That is why the Mozilla Add-ons web site tests all add-ons (including any updates) before accepting them. It was a good idea.
Unfortunately, many authors delay releasing an updated version because typically all it does is "bump" the version, the Mozilla Add-ons web site imposes restrictions on the maximum version an add-on can support, a good number of authors release most updates on their personal web site due to the hassles and delays of submitting it to the official web site, and Mozilla Messaging does not notify authors when they changed something in Thunderbird that might break add-ons (such as removing a method from an API).
There is only one type of indexing
There are five types of indexing:
It's important to know which one is the culprit if you have indexing problems.
You may see a lot of indexing messages in the status bar for a couple of days if you have a large profile when you upgrade from 22.214.171.124, or install Thunderbird 3.* for the first time. It takes time to build the search index for global searching and to download all of the messages for a IMAP account in the background. Some email providers (such as Gmail) also impose a bandwidth quota, which can cause attempts to fetch a message to temporarily (and silently) fail until enough time has passed that it resets your quota.
There have been reports that Google Desktop Search (even when you don't use it to search) can slow down Thunderbird 3.
If you see a "Building summary file" message that's due to it rebuilding the index file (*.msf) for a folder. It needs to do that whenever it downloads a new message. If you see that status message for a long time while trying to open the inbox that means the folder is corrupt. See Inbox stays blank.
If you disable global search you can't search
There are four different ways to search:
Which is the best choice depends upon your personal preferences and your configuration. Global search is very useful if you have multiple accounts and don't know what folder the message is likely to be in. The Quick Filter bar is very useful if you know what folder it's in, perhaps because you have organized a folder hierarchy. Edit -> Find is useful if you miss Thunderbird 2's quick search.
Thunderbird looks in the profiles directory to find your profile
Thunderbird doesn't discover profiles by noticing them in the default location. It looks in the profiles.ini file to find what profiles exist and where they are. This lets you store a profile almost anywhere, including file shares. When you create a new profile using the profile manager it updates profiles.ini for you. When you backup or restore a profile using MozBackup it examines the contents of profiles.ini to find what profiles exist and where they are.
Thunderbird can find the profiles.ini file due to it always being created in the same location on your boot drive, based on your Windows username and what version of Windows you are using. That is also why your profiles "disappear" if you re-install Windows using a different Windows username. They're still there, and the old profiles.ini file is still there, but the new profiles.ini file doesn't know anything about them.
See Moving your profile folder for more information.
You can't import messages or address books from a email client if it's not listed in Tools -> Import
Thunderbird has built-in support for importing messages and address books from a few email clients if it detects they're installed. However, you can use add-ons such as ImportExportTools to import folders if they're stored as mbox or .eml files, and you can use Tools -> Import -> Address Books -> Text files to import an address book if it was exported as a .csv or .ldif file. See Importing and exporting your mail for some other methods, and instructions for other email clients such as Windows Mail, Mail.App, The Bat!, Incredimail etc. That includes importing from other Thunderbird profiles.
Thunderbird is buggy because it uses too much memory
There are many types of memory. The number Task Manager returns includes memory that is allocated but not used and memory shared with other applications. What really counts is whether you have a performance problem, not what the number is, or how much larger it is than with Thunderbird 126.96.36.199.
However, a good rule of thumb is that if you use 150MB or less of memory with Thunderbird 3.* you don't have a memory problem, while if you use more than 250MB you probably do. It can be due to a bug in Thunderbird, in one of the add-ons, your anti-virus scanner or firewall, a problem with one of the SQLite databases etc. It's easy to just blame Thunderbird but usually your configuration is at least part of the problem. See Memory Usage Problems for a checklist that might help you isolate the culprit. A good first step would be to temporarily run in safe mode (not to be confused with Windows safe mode) to disable all add-ons and disable your anti-virus program from scanning messages. Set View -> Message Body As -> Plain text , make certain that View -> Display Attachments Inline is not checked, and don't click on any links or open an attachment while your anti-virus program is disabled.
Process Explorer is a useful tool to see what files are open, what DLL's are loaded, and more details about how much memory is used, if you are technically inclined. See  and  for some tips on using it.
Thunderbird will create your account for you
You need to create an account with your email provider before you create the corresponding account in Thunderbird. Otherwise you don't have a mailbox on the mail server and no permission to use the mail server.
After creating the email account with your email provider you need to describe (define) that account in Thunderbird. That means providing information on how to call the mail server. The settings entered into Thunderbird specify whether it's a POP or IMAP account, what mail server to use, what username/password etc.
IMAP accounts should have the same menu commands as POP accounts
POP and IMAP accounts are quite different. You read new mail in a POP account by downloading it from the inbox. It has a very download-centric view of the world. You read a new message in a IMAP account by opening a remote folder on the server. It only downloads message headers. It has a client-server view of the world. That's why you can do things such as read mail in all of your folders and upload messages.
A POP account needs settings such as "keep messages on server" because, by default, it downloads them to the hard disk and may delete the original (it depends upon the "leave message on server" setting). There is no need for those settings with an IMAP account because it keeps the message on the mail server when it reads it. It fetches a copy which it stored in memory, but never stored on the hard disk.
Tools -> Server Settings -> Synchronization & Storage -> "keep a copy of all messages for this account on this computer" is something completely different. It creates a optional offline folder in the profile which has a copy of the folders messages. You can't read those messages unless you're working offline and they had no effect on whats stored on the mail server.
Deleting a message in Thunderbird has no effect on the messages on the mail server
If you delete a message in a POP account it frequently doesn't delete the original message on the POP mail server. The original message might have already been deleted when you checked for new mail due to "leave message on server" not being checked, or you checked "leave message on server" but didn't also check "until I delete them".
However, if you delete a message in a folder in a IMAP account it always deletes the message on the IMAP mail server due to the differences between POP and IMAP accounts. POP accounts are download-centric, you read mail by downloading it to your inbox on your hard disk. IMAP accounts access (remote) folders on the mail server as if they were local folders. That's why they don't have a setting to "leave message on the server".
IMAP accounts have a lot more features than POP accounts, but they're not a superset. Because they work so differently you can shoot yourself in the foot if you try to treat them as a POP account.
Thunderbird creates every error that it reports
It doesn't. Usually it's just passing on an error message from the mail server if you're checking for new mail or sending a message. Some giveaways are it mentions the name of the mail server, some protocol command (STAT, RETR, LIST, DELE etc.) or says to contact your mail administrator. Some examples:
Error messages about the inbox being full are tricky. Usually they mean the inbox folder in your mailbox on the POP server has so many messages that the mailbox is full, due to you checking "leave messages on server" and not checking something like "for at most X days". In that case you need to use a browser to login to webmail and delete some messages. However it could also mean Thunderbird couldn't download the messages because the inbox folder in your profile is full. In that case you need to compact the inbox folder. It depends upon the details in the error message.
You can always enable POP3, IMAP or SMTP logging per Session logging for mail/news , repeat the problem, and look in the log file with a text editor to see exactly what the mail server returned.
Offline folders are the only way to backup an IMAP account
Offline folders let you read messages in IMAP accounts when you're working offline, and provide a backup. However, you could:
Local Folders are just a waste of space
Local Folders only take a few KB if you don't use them and are useful if you ever need to store messages outside of your account. They are required if you ever want to use "Send Later", send messages in the background, or use a Global Inbox. Figuring out everything that uses them is like playing Whack-A-Mole. If they bother you either keep them minimized in the folder pane or hide them using the MailTweak add-on.
You don't need to automate compacting folders
When you delete a message it's not actually deleted, it's just hidden from view and marked as deleted. It's not physically deleted until you compact the folders. This is a common tradeoff to improve performance. If you have a folder with lots of messages in it and frequently delete messages in it (moving a message copies it and then deletes the original) it's very prone to corruption. Usually this is an issue just for the inbox folder.
Think of compacting as a form of preventative maintenance.
The problem is that it's hard to gauge how often is enough, and the downside of guessing wrong can be very bad. If it's mildly corrupted you might be able to fix it by rebuilding the index or running Cut MboxD on it. If not, it's a lot of work to try to recover messages by editing the mbox file. If a folder is badly corrupted it's possible to lose everything when you compact it. That's because the bookkeeping is all messed up. When Thunderbird physically removes one of the deleted messages (when it compacts the folder) if it can't find where that message ends it might delete everything after it. That's a worse case scenario (which periodically happens).
It's safe to recycle an existing POP account if you change email providers, rather than creating a new one
Thunderbird uses an account specific directory to store the folders for an account. It's name is based on the mail server name, with a numeric suffix added if you have more than one account using that mail server. For example, normally the folders for a Gmail POP account is stored in ..\Mail\pop.gmail.com .
If you switch email providers and edit Tools -> Account Settings -> Server Settings to use a different mail server, it's going to create a new account directory and your old folders will disappear. However, the old account directory and all of its folders still exists, it's just not used anymore. There are two workarounds:
It's safest to create a new account, get it working, copy the messages from the old account and then delete it when replacing a email provider. Another way to avoid problems would be to move all of the messages to local folders before recycling the account.