Certification

Certification services, like Goodmail, Return Path and ISIPP, certify that certain email senders comply with the services' standards. When sending certified mail to an ISP that subscribes to that service, certified senders receive prioritized treatment and may bypass certain spam filters.

For the vast majority of senders certification does not make a lot of sense. The real benefits to certification are the screening and correction process that all the companies have you go through before you are certified. Companies who are certified, will see an increase in delivery, but this increase happens even at companies that do not use the particular list.

There are some areas where certification makes sense, banks or legitimate pharmaceutical companies (Pfizer comes to mind) can benefit from the certification process. But these are specific cases. Generally, if senders are following best practices and aren't sending out large volumes of mail similar to that sent by spammers (say bank phishes or pills) then sending relevant, wanted email will get good delivery.