We run a web and email hosting service for small businesses in the area. One of our customers is complaining of undelivered emails from certain domains (linkedin.com, dyndns.com, salesforce.com). Our server hosts multiple domains, including our own. I tested that the domains in question could email our server by signing for accounts myself and receiving the confirmation emails. Everything worked correctly. There is no entry in /var/log/maillog for the emails in question.
Why would these emails be delivered to one account (hockson.com) on a server, but not another account (castillolanguageservices.com)? Hockson.com is the primary domain for the server.
I also have a message in the mail queue stating that a server configuration error occurred (4.3.5). I am using Postfix 2.6.5 on Fedora 12. The needed firewall ports are open (ie: 25 plus the ports for POP and IMAP).