Sendmail trouble with relaying

[Erik Dörnbach <doernbach@elge.de>]

Hi,

some question, I have a sendmail box running for a number of virtual domains, our main domain is say "aaa.com". I just noticed some funny things starting here, there are some guys using our server against us, by simply opening an smtp connection to us, pretending to be "someone@aaa.com" and sending mail to "someoneelse@aaa.com" - sendmail doesn't see this as a relay or abuse by default.

How can I make sure the only hosts allowed to send in the name of "aaa.com" belong to a certain network/IP range? Guess I missed out a feature or something? Also how can I avoid having mail with empty sender addresses entering the queue?

Thanks for help,

Erik