is there a way to set mail so when I erase a piece of mail on my Mac it will erase on my phone?
iPhone 13, iOS 15
Emails do not sync between devices.
Each device syncs to the email client server using the internet. Thus if one device is not connected to the internet it may not sync with the client-server and will not refresh with the actions taken on the other devices. They need not be on the same WiFi.