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...
it's a complicated problem
it's a complicated problem specially with the very complicated config and docs that sendmail provides. What I want is simply disable sendmail to send messages to any email address if that address is not one of the emails I provided in the config. The problem is that the access file doesn't support wildcards.

elaborate?!?
Although I may not provide you the answer, however I feel your problem is quiet interesting for some people.
So how about you elaborate more, frankly I didn't understand what you mean.
So long and thanks for all the fish.