Emails won’t send

Since October 21, I haven’t been able to send emails on my Comcast.net account.  I receive them fine, but replies go nowhere.  I get a message about the wrong imap address and have talked to three technicians.  They have decided it is an issue with the phone.  Apple tells me the problem is with Comcast email, after they went through my phone.  Not sure what to do.  Anyone with similar problem?