Are there other “approval” services for other email providers, like SenderID for Hotmail?

Question

This question comes from: http://webmasters.stackexchange.com/questions/695/how-to-avoid-hotmail-live-rejections-for-legit-large-volume-emailing

I never knew about this for Hotmail and I'm wondering if there are similar services for Google, Yahoo or others. I work on a few newsletter managers and I want to make sure the emails are getting to their recipients.

Answer 1

Coding Horror had a pretty thorough discussion of sending e-mail through code. It includes a reference to the Port 25 verifier that might be useful.