Mailing List Archive

I have a server which acts as the company outgoing mail server for bulk
info (mail.mx.mydomain.com). We have another server
(server1.mydomain.com) which is used to gather database info and send
mail, using a simple perl program, then connects and uses the
mail.mx.mydomain.com for delivery. And we have our global company mail
server that our employees use for all the company mail (mail.mydomain.com).
For sending our newsletters, promotions, etc, we use
server1.mydomain.com to gather our client info, then it connects to
mail.mx.mydomain.com and sends the mail. In the headers that we
obviously control, what should the "helo" be set to? Should it be
server1.mydomain.com or mail.mx.mydomain.com or can we use
mail.mydomain.com?
Here's what we currently have it set to, not sure if this is correct or
if we should change to something different to be fully compliant:

Received: from server1.mydomain.com (HELO mail.mydomain.com) (a.b.c.d)
by mail.mx.mydomain.com with SMTP; 1 Dec 2013 15:01:37 -0000


And which fqdn should a.b.c.d match? The Helo or server1?

Any help would be appreciated, Thanks.
K