Q: Mail preview text flickering in MacOS Sierra

There have been reports with flickering reported during the beta. You need to report it to Apple Feedback so it can be logged and put in the queue to be fixed. Be sure to give specific info on your Mac. They will need info you'll find about your Mac in “About this Mac”.

http://www.apple.com/feedback/macosx.html

I have this problem. When 1st load up Mail the preview pane shows the e-mail. However as I switch between folders then the preview disappears. Opening the e-mail then takes a very long time.Very annoying and almost makes mail unuseable.

I have the same issue. macOS Sierra 10.12.  I'll report the issue.

I too have the same issue, as well as some of the attachments not showing. macOS 10.12.

System Preferences > Accessibility > Display

Check

• Reduce motion
• Increase contrast

Does this help?

Restart in Safe Boot mode and test Mail. Do the problems go away while booting in Safe Boot mode?

Safe boot

* shutdown

* start the Mac and *wait* for the startup chime to sound

* after the sound, press and hold down the shift key

* keep holding and *wait* until the grey  Apple logo appears

* now release the shift key and just wait (it could take a few minutes)

* eventually the login screen appears with the words SAFE BOOT in the top right of the window

* continue to login to see if the problem goes away.

If the problems went away while in Safe Boot, download and run Etrecheck.  Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here (and recommended by Apple Support personnel) in the ASC to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

http://www.etresoft.com/etrecheck

I have this same problem after upgrading to Sierra.  I did reboot in safe mode and the problem went away, even after rebooting normally.  

I'll keep my eye on this and see if it comes back and post here.

Problem came back in minutes.  Quitting Mail and reopening it makes the problem go away.  I'm sure it will come back again.

Just switching between messages in the Preview pane makes the flicker happen.

The only way I resolved this was to reload Sierra.

Hey IHaddow.  Did you do from your time machine backup, or did you have to trick the Mac into installing it again by deleting the Receipt file?

Steve, I did a soft reinstall, so no need to use my back up.

How is that done?  Thanks.

I just installed it as I had done in the first place. It then gave me an option to either wipe all date or not.

Great.  I just went to the app store and it doesn't even show it as a recent upgrade or list it in my purchases.  Weird.  I'm downloading it now.

Good luck. It took hours to complete !! Maybe down to my broadband connection.