Help with spammers

[Ivan Mirisola]

Hi all,

I have been using MailScanner (without SpamAssassin) for quite a while
and I have a question for you guys.

What is the best way to block e-mails when they are in the form of

[0-9]@mydomain.com

I want to block any e-mail that arrive for invalid users on this
particular domain where user name consists of just plain numbers like:

9827492364236438623896 at mydomain.com

Is this a job for MailScanner or for SpamAssassin ?

Thanks in advance.

Sincerely,
Ivan