After suffering through slow and terrible performance with Thunderbird mail client (11.x and earlier), I did a bit of research to speed up accessing IMAP-based emails. Here’s what worked:
- Disable Preferences -> Advanced -> General -> Enable Global Search and Indexer (Simply Uncheck the box)
- In the account settings, <Account Name> -> Synchronization and Storage -> Keep messages for this account on this computer, uncheck this box. (If you need to keep copies of your IMAP emails, this should remain checked. But ask yourself why you would want to do this?)
- Set the following at Preferences -> Advanced -> General -> Config Editor:
- browser.cache.memory.max_entry_size: 32768
Pleasant performance boost resulted from the above tweaks. Good luck.