We have begun receiving quite a few of the following queue errors:
451 4.4.0 Primary target IP address responded with "421 4.2.1 Unable to connect." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts or delivery failed to all alternate delivery hosts.
The email status in the queue are:
400 4.4.7 Message delayed.
- We use Postini for inbound email.
- We have our own server we use for all outbound email (which are the ones generating these errors).
- I am able to connect directly to the MX servers that are generating these errors via telnet and send email.
- Our reverse DNS lookup for our email server resolves properly.
- Our SPF record tests successfully.
- We can receive email from the domains in question.
- We do not filter outbound email traffic.
- We are no appearing on any blacklists (both the postini mx records and our internal exchange mx record).
- DNS ONLY shows MX records for the postini servers, not the internal server.
- The internal server domain does NOT match the external DNS or RDNS FQDN (email.internaldomain.org vs. email.ouroutsidedomain.org)
Any help would be greatly appreciated.