Mail issues in Sierra

I’ve upgraded to Sierra, and have two issues with Apple Mail. First, I can’t find a way to auto delete sent messages after a month, which was configured prior to Sierra. Second, an empty window appears every time I open Mail, which I have to close. How can I prevent that and automatically delete old sent messages?

There’s no longer a setting in Mail’s preferences to achieve this. In an account’s Mailbox Behaviors’ tab, you could set sent messages to be saved in the Deleted Messages mailbox and have those erased after a month, but this carries the risk that you might accidentally erase things early. The blank window problem has occurred in the past when Mail had been upgraded. It’s the remains of the Welcome to Mail splash screen, which should have been turned off after the upgraded app ran for the first time. A trick that has fixed this previously is to open Mail, disable all accounts, quit Mail, open it again, re-enable accounts, quit the app again, and finally open it a third time.

If the window remains, you may be able to kill it by trashing Mail’s preferences file, but that would create more work to configure the app again. You may find it simpler to live with it for now. Let’s hope a future update to Mail will do away with this for good.