It could be both but i’m most certain it has something to do with the DNS settings on the account domain. Note that if you have a POP3 account you wont be able to receive any until you use a POP3 downloaded. If you have a catch-all account for instance, the domain account DNS should be pointed to the SMTP server. I use NO-IP services for this system on 7 servers. Everyone is happy and no complaints so far.