How many mails are being synchronized with Google? each and every one has to have it's status periodically checked. Then most windows users have an anti virus product that chokes on large IMAP account and it drops off to sleep taking Thunderbird with it. Even if it does not choke, it can double or triple the time it takes to synchronize mail.

BTW your reasons for changing from pop to IMAP are exceedingly poor. Google lied to you about how secure things are and you just complied.

Thanks, I have now deleted a whole load of old emails and things have got much better (I did this before your post). I know that Google lied to me, but it's nevertheless frustrating to get the warning messages every day.

quilkin said

I know that Google lied to me, but it's nevertheless frustrating to get the warning messages every day.

Yet I have had maybe two warnings in the past couple of years that my security with them has issues. No warning messages everyday. How did you get them?

I got a series of emails from Google: Sign-in attempt was blocked [chrisfearnley1@gmail.com] Someone just used your password to try to sign in to your account from a non-Google app. Google blocked them, but you should check what happened. Review your account activity to make sure no one else has access" This happened every day for a period, then more erratically.