Spam sent to me from my own mail server ?

[Chuck Swiger]

On Aug 27, 2008, at 7:38 AM, Peter Ulrich Kruppa wrote:
> for some time now I keep receiving spam mails from my own (small)  
> mail server, some of them with faked usernames some of them even  
> with my own (ulrich at ...).
>  1) How is this possible?

Forging email headers is trivial.  You can do it with telnet by hand,  
although spammers tend to use malware which blasts lots of messages....

>  2) What can I or do I have to do against it?
> I am running a quite plain sendmail setup from 7.0 -STABLE.

Configuring anti-spam measures is something that would occupy a book.   
For starters, look into greylisting, RBLs, and anti-spam tools which  
hook into the milter interface.  There's also some config-level  
changes documented here:

   http://www.sendmail.org/m4/anti_spam.html

Regards,
-- 
-Chuck