qmail help

qmail headers and domain names

[Listening To Music]

Hi!

My server has 3 domains: a.com, b.com, c.com
Whenever a message is sent from my server, the header will contain a line which says:

from myhomeaddress.com (HELO?192.168.1.1?) (123.456.789.101) by a.com with (DHE-RSA-AES256-SHA encrypted) SMTP; 25 Apr 2006 06:45:41 -0700

The a.com part is what I have a problem with. That a.com will change at random to any of the domain names I have on my server. So sometimes it may send a.com in the header, while others it may send b.com or c.com. I'd like to stop this from happening. I know it can be done since:

echo To: [e-mail] ¦ /var/qmail/bin/qmail-inject

sends an e-mail without that header line included. So somewhere in the qmail process, it gets added.

Does anyone know how to prevent this from happening?

Thanks!