I’ve been keeping up with authentication for about 2 years now from SPF to SenderID to Goodmail and Domain Keys. It all seems a bit like bribing someone to let you in the inbox?
As far as I know at the moment, SPF was something that was suppose to save the day but did not work, SenderID was SPF 2 and you pay quite a lot of money to get better deliverability although I am not sure how they measure you to see if you qualify or you just pay more to spray – although Return Path have altered their services and packages lately but I find it very hard to actualy find out the details without holding a phone call with a sales person.
Goodmail seems primarily AOL based and you have to have 6 months on dedicated IP/range of IPs before they’ll consider you and then you pay to per email.
Domain Keys, was a Yahoo creation to help them handle the amount of spam they were getting because they could not handle the volumes. It seems pretty easy to administer and people like Google seemed to have incorporated it well. From not really getting too tekki on it, I am struggling to see, at the top level, how different it is from the old SPF records. Someone has to administrate the applicants and reputation yet it is free?
Personally, if you are sending good emails consistently you should get in. The 3 of the big four: Yahoo, AOL and Hotmail will assign your IPs a reputation based on recipient actions and that reputation will define how many and how quickly you can send to them per IP. So if you are spot on you have nothing to worry about.
Google has recently pidded AOL for the 3rd spot but I have not as yet got much information about their reputation technology. They appear to have been coping very well with the most advanced content filter on the free inbox market but at this size they must have something and logic tells me it cannot be far off what everyone else has done but it wil probably be better than everyone else’s soon!