[Dovecot] Emails from invalid local accounts

[Steven Kiehl]

Hi,

I'm using dovecot 1.2.9 in a postfix/dovecot setup and I'm having issues
with receiving spam where the "from" header contains an address like
accounting at mydomain.com.  Is there some way I can filter out these emails
coming from outside our network with an account associated with our network
which doesn't exist?  Do I just need to configure some custom process to
evaluate these addresses, or is there some way either in dovecot or
spamassassin to do this?

Thanks,

Steve K