nanog mailing list archives

Re: Is your ISP blocking outgoing port 25?


From: John Levine <johnl () iecc com>
Date: 18 Jun 2009 20:18:49 -0000

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
know.

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.

R's,
John


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