For a few weeks I have been having difficulties sending e-mails to @verizon.net recipients. The error that comes back from our mail server is:
"Deferred: 450 Requested mail action not taken-Try later:sv28pub.verizon.net"
Our server attempts to send the message for 5 days until it eventually times out and drops it from the queue.
I have googled the error and found out that there are other people out there experiecing the same problem. Some of them were using MacAfee firewalls. I am not using any type of firewall except for an access-list on our edge Cisco 3600. The rules in the firewall have been the same for almost 4 years. Absolutely nothing has changed on our end that would cause this.
To troubleshoot, I have telnetted to relay.verizon.net on port 25 and issued basic SMTP commands to see exactly where the message is failing. When I issue "MAIL FROM: address@ourdomain.com, there is a ~30 second delay, and Verizon's server responds with the error message above. If I enter other "mail from" addresses, such as gmail.com, yahoo.com, comcast.net, the server responds with an OK, good to go message.
I am running BIND named for DNS on our domain and /25. I have PTR records for every single IP address. I have a proper MX record which resolves perfectly from outside our LAN. Again, nothing has changed on our end.
I would assume that it is not a BlackList issue as I think a more "spam like" message, such as a 550 message, would come back as soon as it saw mydomain.com as the sender of the message. However, it could still be the case. My next step is going to be to contact Verizon to see if they can check to make sure our /25 is not on some type of BlackList.
I have also tried the telnet test to relay.verizon.net, from a different network (Comcast's) using the same "mail from:address@ourdomain.com" command, yielding the same results. Other domains, gmail, yahoo, hotmail, all worked properly. This leads me to believe there is some type of DNS resolution issue with my domain name or there is some type of blacklist problem.
Upon every e-mail sent to user@mydomain.com, my Red Hat box queries about 10-12 blacklists. I would assume that it would not be an issue with my blacklists, as the messages I am having trouble with are outgoing, not incoming. But, both incoming and outgoing would still be using the sendmail service, so I guess I could try commenting out one BL at a time.
Has anyone else seen this issue? Any suggestions?
Thanks in advance.
