We had a problem with email not being delivered to various domains, the senders received a Soft Bounce. Here is an example of the email that was received by the sender:
Your message did not reach some or all of the intended recipients.
Subject: RE: DBA701 - Urgent
Sent: 4/13/2004 5:39 PM
The following recipient(s) could not be reached: 'test@testdomain.com on 4/15/2004 6:00 PM
Could not deliver the message in the time limit specified. Please retry or contact your administrator.
Resolution: We had to talk to the ISP of the receiving end and ask to get Reverse DNS set up for their account.
The problem turned out to be that there were no PTR records set up for the outside IP address. So the email that the sender was sending was valid but since there were no PTR records to go by it wandered off into limbo to die by the TTL. We had to find the problem by doing a search of the PTR records on www.dnsstuff.com using this format
45.123.17.77.in-addr.arpa, the outside address is 77.17.123.45.
Update: Of course now the format has changed at dnsstuff.com and you can just enter the IP address in the Reverse DNS Lookup box. While you're there you might as well get a full DNSReport too.
These errors can be pretty easy to troubleshoot if you use the error codes, You can reference those error codes using this document http://www.unixhub.com/docs/email/rfc1893.txt
4.X.X Persistent Transient Failure
A persistent transient failure is one in which the message as
sent is valid, but some temporary event prevents the successful
sending of the message. Sending in the future may be successful.
X.4.7 Delivery time expired
The message was considered too old by the rejecting system,
either because it remained on that host too long or because
the time-to-live value specified by the sender of the
message was exceeded. If possible, the code for the actual
problem found when delivery was attempted should be returned
rather than this code. This is useful only as a persistent
transient error.
Others have found out that their IP has been blacklisted, Am I blacklisted?
SMTP mail cannot be sent or received in Exchange Server
