How do I set up a email whitelist using only procmailrc to protect my kids from unwanted email?

"procmail can filter by the From header, and there are many recipe examples.

# This one discards all mail sent from the address below.
:0
* ^From: idiot@somehost.com
/dev/null

But don't forget that procmail only works with locally delivered mail. It won't affect mailboxes accessed over IMAP or webmail."

"I think we have not any solution yet, that exactly solves the initial problem. Therefore, I would like to provide a more explicit approach. Lets suppose, that our whitelist looks like this:

white.domain.tld
light.domain.tld

Then I would try the following reciept:

:0
* !^From.*@white\.domain\.tld
* !^From.*@light\.domain\.tld
/dev/null

This would send all emails that are not from somebody@white.domain.tld and not from somebody@light.domain.tld to /dev/null. The remaining emails are send to the default destination. Be aware to use \. in your pattern if you like to match a single dot. The pattern . matches a single character.

If you have a short whitelist, you could try to get an even shorter reciept by combining the patterns:

:0
* !^From.*@(white|light)\.domain\.tld
/dev/null

Be aware to use ( ) here. Using [ ] would be a mistake."