Return Path’s Q2 2008 Reputation Benchmark Report (pdf) found e-mails sent from “legitimate” e-mail servers averaged a delivery rate of 56 percent. 20 percent were rejected; 8 percent filtered out of the inbox. The rest — 16 percent — were bounces.

So nearly half of the time, e-mail marketers’ messages don’t get through. But there are ways to increase deliverability, insists George Bilbrey, Return Path’s general manager of delivery assurance. Here are five:

Yahoo using Sender Score Certified whitelist and Return Path was quietly made public in January 2008, “Yahoo! is implementing the scheme and will begin checking using it sometime in spring.” We have not heard much since. My connection at Return Path just mentioned Yahoo the other day and brought it back to mind.

Return Path blog says “Receivers that accept the Sender Score Certified whitelist include, among others, Windows Live Hotmail, Time Warner Cable, GoDaddy and soon Yahoo! and Yahoo! operated email properties.”

Maybe this is why Yahoo has been such a nightmare to deliver to lately and why Yahoo pulled it’s FBL in March.

Since they announced that Comcast would offer an FBL managed by Return Path I have been expecting the Yahoo Sender Score Certified Return Path full press release to come forth.

I don’t mean to be a nutty conspiracy theorist here, but first Comcast has no whitelist, no FBL and is tough to get your email delivered to. Then Comcast offers an FBL through Return Path. Next, it’s Yahoo, who pulls their FBL, calling it an end to a beta, is impossible to deliver any email to for months and now is poised to solve it all with Sender Score Certified and Return Path.

As always I invite your comments below! = Chris Lang