I have a strange problem. everything has been working fine for a number of months then suddenly, no one could send email. recieving email is ok however.
just the one server
Win server 2008
symantec endpoint protection
the mail queue gives me the below error;
451 4.4.0 Primary Target IP Address responded with:"421 4.2.1 Unable to Connect"
which points me to a DNS error but nothing has changed, have flushed and registered which did not fix it. I did find that I can telnet to port 25 from external to the server but I cannot telnet from the server through port 25. I have tested telnetting to port 25 from a workstation in the same domain and is ok so it has to be the server. I have turned off the firewall and anti-virus just to test but still nothing. I can however telnet through other ports, just not 25.
any help would be appreciated.