Maybe relay?...

[mariat]

Hi, I hope this is the right group to ask this question. I am using Sendmail 8.9 in Solaris. I received an email that bounced back due to an "unknown user" error. It was a spam email and It shows that was send using my server, I am going to put the header but using:
mydomain.com -> as my domain name
myserver.com -> as my server's name
myserverIP -> as my server's IP
othersdomain.com -> The server to whom was send the message and bounced to me.
Here goes the header:
------ This is a copy of the message, including all the headers. ------

Return-path: <help@mydomain.com>
Received: from c-24-125-104-192.va.client2.attbi.com ([24.125.104.192])
by smtp.othersdomain.com with smtp (Exim 4.24)
id 1Bn913-000302-LV
for bprice@othersdomain.com; Wed, 21 Jul 2004 00:47:41 -0400
Received: from mydomain.com (myserver.com [myserverIP])
by c-24-125-104-192.va.client2.attbi.com (Postfix) with ESMTP id B72F98C326
for <bprice@othersdomain.com>; Wed, 21 Jul 2004 00:47:36 -0400
Message-ID: <100101c46edd$b8416daa$93c9db94@mydomain.com>
From: "Referential K. None" <help@mydomain.com>
To: Bprice <bprice@othersdomain.com>

I am worry about my server being open relay. But I went to this web site

http://www.abuse.net/relay.html

and it tested OK, the relaying was denied...So I just wonder if maybe they (the spam guys) are sending their email and showing as if it is coming from my server...Also I sent an email to bprice@othersdomain.com just to see how will be the answer and the first three lines were different, like the following:
Return-path: <help@mydomain.com>
Received: from myserver.com ([myserverIP])
by smtp.othersdomain.com with smtp (Exim 4.24)

Thanks for any help