Go to mail Preferences -> General -> Check for new mail
Change your setting to 5 mts or higher. Or choose "manually"
When you try to quit, it could be active looking for new mail.
Hope this helps. After a couple of years of struggle it worked for me !
In the end I deleted Avast as I had a suspicion it was scanning mail which was preventing it from shutting down properly and it worked first go
The Apple discussion forums are hosted by Apple but depend on community involvement (much like this one). In other words, it's not Apple techs on the other side.Because when I was having problems and was trying to get answers from the Apple.com/mac/ forum, I didn't even get a single reply.
Go to mail Preferences -> General -> Check for new mail
Change your setting to 5 mts or higher. Or choose "manually"
When you try to quit, it could be active looking for new mail.
Hope this helps. After a couple of years of struggle it worked for me !