Hi,@Bob Krivacic
Thanks for posting your question in the Microsoft Q&A forum.Based on your description, I need to confirm a few things with you:
1.Does this problem occur when you send to other users with sbcglobal.com and att.net addresses?
2.When you send an email to a user at another address is it received correctly?
3.What does returned mail look like? Can you provide a full screenshot?
4.Is the type of email account you are using Exchange Online or Exchange on-pre?