User creatin by mail

I wanted to block the user creation by mail, so I looked some modules.

There is one Module, the EmailParser, here there is a Check if
sendermustexistinexternaldatabase and and userfoundinexternaldatabase,
but this sub isn’t called anywhere. Strange.
The script that is called after an incoming mail is Mailfrom, right? So
all checks that are in emailparser don’t work?

Thanks

Samuel Senoner