moltoparticolare wrote:
thanks but I already have the "automatically cc myself" box unchecked. Any other suggestions?
Yes , change it to CC and see if you now get 3 copies in your sent box—this may be telling as you try and isolate the problem.
You do not say who is your email provider— it may be logging in through a browser and checking preferences there...(?)
Uninstall all third party apps that are Cleaners/Optimizers/Anti-Virus/VPN—
all known to cause issues on the macOS
To trouble shoot further you can:
—Try a SafeBoot https://support.apple.com/en-us/HT201262
Takes noticeable longer to get to the login screen, does a 5 minute disk repair before it fully boots up, and certain system caches get cleared and rebuilt, including dynamic loader cache, etc.
Login and test. Reboot as normal and test. Caches get rebuilt automatically.
In Safe mode third party system modifications and system accelerations are disabled, it removes malware, etc hampering smooth operation, however a reboot will put it back to normal mode.
This test will tell you if third party interference; extensions etc are not loaded in safe boot mode.