AOL Updates Spam Filtering

Over on the AOL Postmaster blog, Lili Crowley announced yesterday that AOL has made changes to their spam filtering system. Specifically, more senders may be subject to blocking with CON:B1 errors. AOL’s website explains that CON:B1 errors indicate that an IP address is being  blocked “due to a spike in unfavorable e-mail statistics.” This strongly suggests that a sender blocked with a CON:B1 error message has a negative sending reputation. This is yet another data point as to how ISPs have been tightening up spam filtering and reputation requirements over the past few years. What you might have been able to deliver five years ago, you might not be able to get delivered today.


  1. John says

    Found any advice for a low volume (4K- 20K warmed IP per day to AOL) that was previously inboxed?

  2. Intermittent AOL issues? | E-mail Marketing Specialisten says

    […] a sender. Meaning, AOL is intentionally choosing to block that mail due to a reputation issue. AOL updated their spam filtering algorythms back on May 6, and the net result is that AOL is more likely to block you for spam or reputation reasons than […]


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