I understand an old email draft will open and close when opening the Mail application on your Mac. If you have deleted the message from the drafts folder and it still appears, I would try logging into your mail provider via a web browser and check to see if the draft shows there as well. If it does, delete the draft there and test to see if the behavior persists on your Mac. You can also test to see if the behavior ceases by deselecting the option to store draft messages on the server under Mail > Preferences, click Accounts, then click Mailbox Behaviors.
Mail for Mac: Mailbox Behaviors preferences in Mail
Please let us know if the behavior persists, and than you for visiting Apple Support Communities.
Email App Keeps Popping Up On Mac Iphone
Aug 09, 2019 I ended up dumping Mail.app for Outlook 2016 for Mac. I plan on dumping GMail/GApps in the future since it doesn’t really play nice with Mail.app and I’m not keen in having Google have control of everything and privacy concerns. After removing the accounts, Mail.app didn’t randomly pop up. In short, it may be just a GMail issue. If you use Mail on your Mac, learn ways to solve problems when sending, receiving, and viewing emails. Use information found in Mail in other apps. Delete emails. Print emails. Search for emails. Free up storage space for email accounts. Problems with security.
Dec 14, 2016 7:55 AM