Mail held but then stop router and restart and it works

Everytime I get a mail pending it says it is sending from in Domain: libertydiversified.com. THis was an old domain I had on my server but is now removed I thought. I have looked everywhere.

It is hidden somewhere but don’t know where to look. Having to stop and start router dailing.

Started after I upgraded to 8x.

90% of the time it is fine but the 10% is killing me.

Router: No messages transferred to abc.COM (host abc.COM) via SMTP: Remote system no longer responding

Or:

“The server is not responding. The server may be down or you may be experiencing network problems. Contact your system administrator if this problem persists.”

Thank u.