on my devel machine I have backups for forums and other scripts that has the same database on my live server, if a cron job is executed and it involves sending mail then users get confusing mail from a domain they don't know! I use sendmail only to send outgoing mail, and I can't disable it on the devel machine as I need to test send mail functionality.

What I need to do is disable messages sent with "To:" recipients that is not on list ex: (not) *@example.com, root@email...