Can't receive emails (can send)

Hoping someone can point me in the right direction....I have an email address that hasn't been used in a while. I can login, send email, but I cant receive any. Always sends back an error code. "Invalid email 550 5.2.1 <email[email scrubbed] - removed by OP>... blank mailhost - invalid address, relay=" Spent 3 hours trying to resolve with ATT and then they said I would have to pay them to research more. Sent an email to abuse@att.net that was never responded to. Been thru all settings, it seems to be something on their part, but they have no idea. Ready to get rid of ATT all together at this point.  Similar problems with other users appear to be unresolved in this community

To clarify....I've been trying only thru webmail rather than apple mail, but either way, it wont receive email, but allows me to send.