[cobalt-users] Spam [Raq4r]

["Jon" <jjma@xxxxxxxxxxxxxx>]

Hello

I regulary receive emails sent to Undisclosed.Recipients@xxxxxxxxxxxx and would like to block this abuse from source.
Could someone suggest a way of stopping spammers using this abuse of our mail server? I have created a modified sendmail.cf with
filtering via ordb.org but this doesn't stop the emails for undisclosed.recipients and there are no users called that on the server?

Thanks

Jon