2007 has brought a lot of changes on the email deliverability front.  Most ISPs have moved from a content-focused spam filtering methodology, to a reputation-focused model.  They rely heavily on a sending IP address's reputation when determining whether or not to deliver mail to the inbox.  Now, your sending reputation — and by extension, your adherence to permission — are the main things ISPs use when determining how to disposition the mail you send.

The good news is that authentication technologies such as DomainKeys and Sender ID are finally starting to make a difference — improving delivery and reputation at Yahoo and Hotmail.  Look for more ISPs to start to pay closer attention to email authentication over the next year.  The big ISPs promise that eventually reputation will be portable and domain-based.  Will that actually happen in 2008?  Hard to say, but we're ready and able to support a change like this if and when it happens.

ISP filters, blocking criteria, and sender requirements continue to change as well.  For example, Earthlink now expires dead email addresses after a few months of account closing.  Comcast now has a feedback loop.   And AOL is much more likely to de-whitelist (and block) problem senders than they were a year or two ago.  Look for more changes like this over the next year, and look for us to start incorporating feedback loop, bounce, and reputation data from other ISPs (such as Hotmail) to improve our efforts to maximize your deliverability success.  For more deliverability insight, check out our brand new whitepaper, 2008 Email Marketing Trends.