Via: Recommended IMAP client settings; Google Help
From the Tools menu, select Account Settings and highlight your Gmail address.
- On the Server Settingstab:Check for new messages at startup > checked
Check for new messages every 10 minutes > checked
When I delete a message > Mark it as deleted
Clean up (“Expunge”) Inbox on Exit > leave unchecked
Empty Trash on Exit > leave unchecked
- On the Copies & Folders tab in the When sending messages, automaticallysection:Place a copy in > leave unchecked
- On the Copies & Folders tab in the Drafts and Templatessection:Keep message drafts in > Other
Other >[Your Gmail address] > [Gmail] > Drafts
- On the Junk SettingstabEnable adaptive junk mail controls > leave unchecked
- Click OKto save and close your account settings.If you’d like to to further enhance your IMAP experience, follow these additional steps:
- In the ‘Tools’ menu, open Options.
- On the ‘Advanced’ tab, open the General section.
- Click the Config Editor button.
- In the ‘Filter’ box, type ‘browser.cache.memory.capacity’
- Double-click on the browser.cache.memory.capacity entry to edit its value.
- Change the value to ’30720′ and click OK.
- Delete the text in the ‘Filter’ box and type ‘mail.server.default.fetch_by_chunks’
- Double-click on the mail.server.default.fetch_by_chunks entry to set its value to false.
- Close the ‘about:config’ window and then close ‘Options’ by clicking OK.