We have an SBS machine that we use as our internal mail server.
Recently, we have had a number of emails returned from a number of different recipients. Reasons for non-delivery are time expired or permission denied. These are just one-off emails - not part of any bulk mailing activity.
There have also been a number of emails delayed for many weeks - some sent in August have just been delivered to the recipient.
Some of the recipients are using public services like hotmail - so I assume it's not an issue with the recipient servers.
I've double checked all settings on our server...been to DNSstuff.com to check junk email blacklists and made sure reverse DNS is set up correctly.
Retry intervals on the SMTP server are 10 minutes, expiry after 7 days.
All appears to be as it should.
However, one thing I have noticed is that the Message-ID header on our outgoing emails contains a different hostname to the one sent as FQDN, which is the one registered with reverse DNS.
We have two hostnames pointing to our public IP
Originally, the only host name we used was mail.ourcompany.com and so MX records, SMTP server's FQDN and reverse DNS are setup for mail.ourcompany.com
However, there is a small web application that needs to be accessed by a couple of our customers that runs on our SBS machine - restricted by IP to their offices and also password protected. We have a SSL certificate for this (public CA) under the hostname secure.ourcompany.com.
So this same certificate has been used in the SBS Connect to Internet wizard for use with Exchange.
As a result, the Message-ID header on outgoing emails has the suffix @secure.ourcompany.com and not @mail.ourcompany.com which can be correctly resolved using rDNS.
Would this cause a problem?