Automatic email setup add-on: Gmail IMAP Account Setup THUNDERBIRD VERSION 3 HAS NATIVE SUPPORT FOR GMAIL.
Manual email instructions: Setup Thunderbird according to gmail’s imap instructions
At the bottom of gmail’s instructions you will see “recommended settings“. Don’t follow the first recommendation, regarding deleting. Instead of actually (permanently) deleting email we can have it moved to the Trash folder, as if you were using the gmail web interface. Gmail has strange folders structure in imap. Here are a few steps to work with gmail folders (Of course, they call them labels :-)
Under Account settings -> Copies and Folders
1. un-check “place a copy in… sent”
2. change “drafts and templates” to Other -> [your gmail address] -> [Gmail] -> Drafts
Note: Sent and Drafts will automatically show up in their respective folders, as long as you send mail through smtp.gmail.com.
3. Go to Options/Preferences (under tools or edit menu). Go to Advanced -> Config Editor. In the Filter box, type “mail.server.server” and look for the gmail address. Whichever number is in the X place of mail.server.serverX, is what you want to use for the new value.
Right click New -> String “enter mail.server.serverX.trash_folder_name” (X is the number that correlates to your gmail account, from above). Next enter “[Gmail]/Trash”. Restart Thunderbird. Delete something, if it does not go into the [Gmail]/Trash folder restart again. It should work after that. Now you can delete the Trash folder (represented as [Imap]/Trash in gmail)
Contact syncing: A few options.
A very popular and stable add-on Zindus Its great but does not support the address field syncing. (Enter your user/pass under Tools -> Zindus)
gContactSync has support for the address field but is very early in development. If any contacts have an empty email field it adds a @nowhere.invalid email address in Tbird. Thankfully this is not synced to your gmail account!
Also, This looks promising but does not work with Tbird3 Google Contacts.
BACKUP CONTACTS BEFORE SYNCING!
Calendar Sharing: Use the add-on Lightning (aka sunbird as a Tbird add on). Lightning 1.0b1 does not integrate with Thunderbird 3 toolbar layout very well. It messed up the “file” “edit” and “view” menus. Although, they aren’t really missed by anyone and are sort of accessible if you really need them. Try it for yourself, its not too bad.
For native support follow the Google sunbird instructions for CalDav (recommended)
There is also another plugin called Provider for Google Calendar that can be used..