Spam sent to me from my own mail server ?

[Peter Ulrich Kruppa]

Hello,

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

Thanks for your answers,

Ulrich.

-- 



Peter Ulrich Kruppa
Wuppertal
Germany