Just this morning the entire company stopped receiving external emails. Sending/receiving internally works fine, sending externally works fine, receiving external does NOT.
Only a single NDR recieved out of the hundreds of test emails I sent to myself.
Reason: Remote SMTP server has rejected address
Diagnostic code: smtp;550 relay not permitted
Remote system: dns;nature.naturesvalue.com
Another funny thing I noticed is, I recieved 2 of my test emails after a 40 minute delay but nothing after that.
I don't recall changing anything on the Exchange server but if I did, what could be preventing external emails from coming in?
We're behind a Firebox Fireguard NAT router and according to dnsstuff.com, the MX record for naturesvalue.com is pointing to our router WAN IP (as it should, correct?) but according to dnscheck it does not find an MX record at all.
Incoming SMTP is allowed and being forwarded to the correct internal IP of the Exchange server. SMTP for outgoing and optional network is allowed as well. However I cannot telnet port 25, possibly an issue with the firebox?
I've spent literally hours researching and I just can't seem to find any resolution.