For a long time, my wife and I had an email addresses of firstname.lastname@example.org and email@example.com. I decided to get my own domain and email and now our email address are firstname.lastname@example.org and email@example.com. The incoming mail server is imap.mydomain.com The outgoing SMTP server is smtp.mydomain.com My email works great. However, if someone sends my wife an email they get a notice that the "Mail Delivery Failed". The following address failed: firstname.lastname@example.org. SMTP error from remote mail server after RCPT TO: email@example.com. BUT, my wife does in fact get the email. But the sender doesn't know this. I've looked at my wife's settings on her Macbook, and there is no SMTP server for Cox. I deleted it when I changed emails. One more bit of weirdness. If I send my wife an email from my work email address, I get the Mail Delivery Fail message, although my wife does get the email. I get her reply too. But if I send her an email from my firstname.lastname@example.org address, I don't get the Mail Delivery Failed message. I'm stumped. Any ideas what the hell is going on? Cox is like a bad penny.