When I did a new installation of Fedora 13 and configured Thunderbird 3.0.4 for IMAP, I found that the performance was just atrocious. It was downloading all the messages from all my folders.

The release notes for Thunderbird gave me a hint:

IMAP Folder Synchronization

Thunderbird will download IMAP messages by default in the background to allow for faster message loading and better offline operation. This feature can be enabled on an individual folder basis via Folder properties, or for all folders in an account via Account Settings / ‘Synchronize & Storage’.


I turned this “feature” off for my account. It is in “Account Settings” and then “Synchronization & Storage” for my IMAP account. From here, I unchecked “Keep messages for this account on this computer.” Also, I changed the “Disk Space” setting from “Synchronize all messages locally regardless of age” to “Synchronize the most recent 1 Weeks.” These two settings made a huge improvement to my performance. Yes, I lose offline access, but that does not matter to this desktop computer.