Sent email keeps moving itself to Inbox

Hello rob.phil,

Is this specific to a single email or does it occur with random sent messages? Also, what type of email provider does this involve? We don't want the full email. We just want to confirm the provider.

As an additional test, could you run the Connection Doctor and let us know if there are any alerts? Here's how, per Use Connection Doctor in Mail on Mac - Apple Support.

1. "In the Mail app  on your Mac, choose Window > Connection Doctor.
2. Review the status information.
3. If you’re connected to the internet, there may be a problem with the account’s mail servers or your account setup. Follow the instructions shown in the Details column. To quickly display the account in Accounts settings in Mail, double-click the text in the Details column.
4. To show log information while Mail tries to connect to mail servers, click Show Detail, then click Check Again.
5. When you’re done, click Check Again to verify if your actions resolved the problem.
6. If the problem persists, contact your email account provider to verify your account details and setup."

Thanks!

This may seem overly simplistic but my question is: Do you have 'Automatically CC myself' enabled in Mail Settings?

I am seeing this same issue. It doesn't happen when you initiate a message only when responding to a message. I double checked the CC and BCC options in settings that is not the issue. I suspect it may be an undocumented "feature". It seems to have popped up after the latest iOS update.

I have narrowed down to It happens when responding to a message that has been sent to you and you have a couple of rounds of back and forth emails, maybe something to do with subject line repeating and it trying to keep some type of thread in tact? I haven't been able to pin down what combo drives it but it happens pretty frequently with back and forth emails. The message is in your sent items in addition to a copy in your inbox. Whatever it is, its annoying, and creates extra emails I just have to delete (if I want to find a sent message that is why I have a sent mail folder). I want it turned off and can't figure out if there is a setting somewhere.

Or Bcc as well: