Is your ISP blocking outgoing port 25?

John Levine johnl at
Thu Jun 18 20:18:49 UTC 2009

>I wonder which ISPs are still doing so. I know comcast has been doing
>that but they cancelled it after many complaints. It seems to be the
>same case for Verizon.

You're mistaken.  Comcast most certainly does port 25 filtering,
although not necessarily on every line at every moment.  So does
Verizon, AT&T, and every other large North American consumer ISP I

Look, kids, it's not 1998 any more.  These days outgoing traffic to
port 25 is approximately 99.9% botnet spam, 0.1% GWL, and 0%
legitimate mail.  Blame the botnet herders and the vendors of cruddy
software that year after year still is full of trivial exploits.  If
you can make the botnets go away, I will be happy to lead the charge
to unblock all those ports.

If it's important to you to have an unfiltered connection, pay for
business service that has a static IP, or arrange to tunnel to some
host that does.


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