How to Handle Multiple IMAP Accounts in Thunderbird
If you have to setup and maintain multiple/many IMAP accounts in Thunderbird 2.x to deal with having multiple computers needing to share folders, at first it might seem like a special ring of "email hell" called "IMAP Hell". However, with a little help, it isn't so bad.
Thunderbird plugins you should have before setup
* Display Quota
* GMail IMAP Account Setup
* Sync on Arrival (rename .xpi to .zip, unzip, edit install.rdf to change version to make it support up to whatever version you are using, zip it up again (and be sure to zip up all of the files in that directory and not a parent directory or it will fail to install), and rename to .xpi.
Forget local, push to the IMAP server and share it
* You can push local mail to (at least some) IMAP servers regardless of where it came from.
* Count on this potentially taking several - many tries if you have a lot of email (thousands or more), because the client will periodically fail.
* Just continue trying moving sets of messages, but when there are a lot of messages in the IMAP folder, it seems to take a long time to move even a small set of messages.
* Some times are faster than others for doing this.
* You can use search folders + making those search folders favorites in Thunderbird to limit the number of folders you see (only look at your favorites most of the time).
* Create a search on the folder of your choice (ignore the rules for now unless you want to use them)
* Click to save it as a search folder
* Select "Match all messages" if you don't want any rules
* Select "Search Online"
* Save the search as a folder, probably in your Local Folders top-level to make it easier to get to. Note that when you save it gives you the option of selecting folders. This will allow you to have search folders across multiple IMAP accounts. I have one called Sent in my local folder that is a search folder to find all mail in sent mail folders in all of my accounts.
* Right-click on the search folder to mark as a favorite
* Use the arrows above the folder list to switch to the favorite folder listing.
Voila! No more IMAP Hell!
* "Tools -> Options -> Advanced -> Network & Disk Space -> Disk Space -> Compact folder when it will save over 100 kB -> OK."
To Avoid GMail IMAP Timeouts (and Avoid Other IMAP Timeouts) Reduce Mail in Each Folder
* Either delete mail, or better yet, move old mail out of the main folder you are checking into other folders (if you can- be wary that GMail uses "tags", not really "folders" even though they appear to be IMAP folders to the client. This is intuitive for GMail itself, but not helpful for those trying to reduce folder sizes as it can mean the emails don't really move, but just new "tags" created, making it look like you only copied the email).
* Follow these instructions if Gmail delete doesn't work in Thunderbird. Basically, instead of [Gmail]/Trash as the string value in config editor for mail.server.serverX.trash_folder_name it should be similar to: imap://email@example.com/[Gmail]/Trash. Note that as soon as you delete something it is GONE from all Gmail "folders" even though it might show up as a crossed out email until you go to a different folder and then come back to it.