Ok I apologize if this post is a little vague. Right now I don't have any of the bounce back messages with me to give a specific example of what I'm about to ask.

I've been running a Postfix mail server for about 10 months now. The thing works great and "it" never seems to have a problem. It also never seems to have a problem receiving mail from other Linux mail servers.

I'm using a lot of the Postfix client/sender restrictions. ie: reject_unknown_hostname, reject_non_fqdn, etc. This seems to cause a lot of problems when someone tries to send me an e-mail from an Exchange server.

I've never configured Exchange, and I get the feeling that I'm having issues receiving e-mails from Exchange servers with, well, not so knowledgable administrators. The issue seems to be that the Exchange servers' hostnames don't have DNS entries.

For example, let's say domain.com is being hosted on an Exchange server. The Exchange server's hostname may not be domain.com, it may be cc-exch-win2k3.domain.com. Now domain.com will more than likely have an A record in the company's DNS, however, if they do not include a DNS record for cc-exch-win2k3.domain.com, then my Postfix server will reject the message. The Exchange sender will get a bounce back saying that cc-exch-win2k3.domain.com hostname was unknown.

So is this my fault? Should I just remove the reject_unknown_hostname from my Postfix restrictions? Or is it the job of the Exchange administrator to make sure that his/her server has a valid DNS entry so it doesn't get flagged as spam?

The other issue seems to be that not many mail servers seem to use tight restrictions. So when I bring this up with the Exchange admin he just says "Well we don't have any problems sending to other e-mail addresses, the problem must be with your Postfix server."

Grrrr....

You might consider using reject_non_fqdn_hostname instead. There's a link to this page on the postfix site. Here's the relevant part:This point of view is expressed in many places, as you can verify with a google search.