Apple Mail sending blank email replies whenever an email is received...

I've been experiencing an issue wherein all emails that I receive have a blank reply sent back immediately, which I didn't create. They are in the Sent items folder, and my customers are calling me telling me that my reply is blank.

This happened in Catalina, so I updated to Big Sur and it's still happening. I've removed the account from Mail, restarted, and re-added the account, and still this is happening. I don't have any rules whatsoever, and I've checked Gmail for "rules" and have none there either.

The view-source of the message shows" "Auto-Submitted: auto-replied", and I can't find a setting for that.