This is how I handle “whitelisting” (example for Gmail)

It works for now, and if the spammers work around it, I will just make it a little more specific by using specific information within the headers, or part of the unsubscription notification.

Proprietary Concept: Unique key to prevent spam filtering
To be quite honest, a service like Aweber or Getresponse should be able to add a unique key that is specific to my email address, such as using a base64 encoding with a seed, that would make it impossible for a spammer to replicate, and a 100% guaranteed way I could whitelist all emails they send me forever.
I am licensing my whitelisting key solution under GNU FDL so if anyone tries to patent this idea they get to fight the legal battle.

The following is an example for Aweber mailing lists, but you can do the same for Getresponse, iContact, Feedblitz, Mailchimp etc.

Don’t listen to any service that thinks their delivery rate is so good that you don’t need to whitelist in some way.

This filter method has pulled over 100 emails out of the spam folder of Gmail for me in the last week.

After you have this set up, any emails that might otherwise have gone to spam will have this at the top

I won’t say no to free unlimited email services for solving your delivery problems forever

This example is based around Gmail, but I am sure other services have a way to create filters to prevent things going in spam that override other things.

If all email you asked for made it into your email box, would you have time to read it?