Many people seem to be opposed to email whitelisting, but I haven’t heard any reasons why they consider it such a bad idea.
A couple of years ago, I installed a system called qconfirm (works with qmail), grepped the email addresses out of all my existing mail, and added them to the whitelist.
When I know I’m going to get mail from a new address, I just add the address to the whitelist. In the case of automated systems (forum registration etc.) I don’t even bother doing it until I get the message.
With qconfirm, I can pull up a list of sender addresses and look at the few most recent to find the ‘legit’ sender’s address. Here’s how I do that:
qconfirm list | sort | tail -20
With real people, it’s polite to add them before they send you mail, but the worst that can happen for the un-whitelisted is that they have to read your short apology, press ‘reply’ and then ‘send’.
Adding someone is as easy as this:
qconfirm ac rik@rikkus.info
I now get about 1 spam message per week, instead of 2000.