Back in February, Verizon announced it would start requiring outbound mail go through port 587 instead of port 25 during the next few months. It seemed like a good idea to squelch spam. Most other major ISPs did it. People applauded Verizon for doing it.

Unfortunately, it seems that if it had any effect it was short-lived. Looking at anti-spam blocklists on a daily basis, a couple of Verizon Autonomous Systems (ASes), AS-19262 and AS-701, do show dips in blocklist listings on the blocklist PSBL in March. But they don’t last.

Spammers are very adaptable, partly because the botnets they use are adaptable. Good try, Verizon.

This information is from an NSF-funded academic research project at the University of Texas at Austin business school. Thanks to PSBL for the blocklist data.

-jsq