I have a quick question about mailservers more specifically MX DNS records.

So here is the situation. I have a Hosted MS Exchange server (off server) and qmail (on server). Because it costs money for me to create exchange mail accounts, I would like to keep some of my other email accounts on my linux box. Right now here is my current DNS setup:

mydomain.com. MX (15) mail.mydomain.com.
mydomain.com. MX (10) mail1.exchangehoster.net.
mydomain.com. MX (10) mail2.exchangehoster.net.

But if I try to send an email to notExchange@mydomain.com the exchange server returns a does not exist and sends a rejection notice. My understanding of MX records was that it would attempt all MX records (regardless of priority) until it failed on all records. But that is not the case.

Can somebody help me with this problem?

MX priority values only come into play if the higher priority server cannot be reached
DNS plays no part in delivery to the mailbox.

What would be recommondation to fix it? I am assuming I will have to modify qmail in some way, but I am not familar with building or configuring qmail. Also it is worth noting that qmail is on a multi-site server, so it would have to be domain specific.

Thanks

A google search turned up this thread, http://forum.qmailrocks.org/showthread.php?p=20760