I just obtained a new client today and the first issue they want me to work on is to determine why they can't receive external e-mail, but can send to external and send and receive to internal. I setup a test account on their server and then sent the test account 4 e-mail from my server and sure enough they didn't go through. I looked at the queues on my server and received the following error: 452 4.3.1 insufficient system resources (see screenshot below)
So then I opened the queue on their server and it is a mess; a ton of e-mails attempting to be delivered (see screenshot below).
I ran their domain through DNSstuff.com, and everything reports back ok: no open relay, spf records, etc. They are listed a few RBLs, but these are the extortion ones. (see screenshot).
I am at a loss as to what this could be. Any help would be greatly appreciated.