I see recipients of my mailing showing as "expired". What does that mean?
Expired status for a mailing recipient means the recipient hit the 4.5 day (by default) limit without being successfully delivered, but we also did not get a reject message from the receiving server.
This is typically caused by one of the following:
a.) There is no valid MX record posted for the domain
b.) The server that the MX records for the domain resolve to do not accept any mail connections