Sierra Mail Slow

Thanks - combining this with a rebuild and then restarting Mail fixed the slowness.n

Thank you very much pawciu.

Has sorted mine out too.

pawciu is a genius!

Not sure if this will help, and maybe I should have realized it before, but when I click and hold on the Mail icon in my dock, it showed like 10 versions of the viewer window. I then hit "show all windows" and noticed small thumbnails of the viewer windows at the bottom of my screen. I clicked on each then hit Command + W to close them out one at a time. This seems to have sped my mail up considerably. I also did all of the things recommended here. Turned off the "highlight messages with color...", rebuilt the inbox etc... So maybe it all helped!

Fact is since 4 Weeks Apple does nothing about it!

In Mac OS El Capitan Mail worked flawlessly!

Windows will eat Apple soon!

Sorry but truth is I think they are working on this, I received a call from Mac support (unsolicited) following up on this error. Contrary to popular belief they have a team that monitors these forums for issues and future bugfixes so are aware of the work around and have informed me that they are developing the fix, I agree that this should have happened sooner and am sure that there are many customers who dont know about this workaround but I guess this is what happens !

I also received a call from Apple Support to get information about how pawclu's solution was affecting Mail on my computer. Personally, I don't miss having mail threads highlighted. I think Apple engineers are aware of the problem and at least gathering data on why some computers/users are being affected.

Thanks a lot. Have been desperately looking to find a solution for my sluggish Mail app after the update to Sierra. After many unsuccessful attempts, your suggestion fixed the problem right away!