A full 22% of all permission-based e-mail was blocked by the top Internet service providers (ISPs) during 2004, according to a Return Path study.
Corporate e-mail mistakenly considered spam by ISPs is a growing problem, up 3.3% over the second half of 2003, noted Return Path.
Return Path monitored 50,000 marketing and transactional campaigns through its Mailbox Monitor service between Jan. and Dec. 2004. Blocking for each campaign varied from a low of 1% to a high of 57%.
In addition, blocking rates varied widely by ISP from a low of 5% to a high of 36%. Companies saw the best delivery success at Earthlink, BellSouth, and CompuServe, which blocked only 5%, 6% and 8%, respectively. The most blocking and filtering (36%) occurred at RoadRunner, followed by Mail.com (34%) and Comcast (31%).
The ISPs monitored represent more than 80% of the mailing lists for most corporate mailers, said Return Path.
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