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Re: [Nmh-workers] Verizon DSL block

From: Ken Hornstein
Subject: Re: [Nmh-workers] Verizon DSL block
Date: Fri, 22 Jan 2010 17:12:58 -0500

>> The port 25 block is pretty much standard for large ISPs today; it's
>> to prevent spammers from using massive networks of compromised PCs to
>> deliver spam.
>Changing ports is useless unless authentication is required.
>If deterring spammers is the primary goal, then ISPs can just require
>authentication for customers over the standard SMTP port.

I'm not really here to debate you on this ... but the _point_
is to prevent zombie PCs from doing final delivery to random sites
on the internet.  It's a lot easier for the ISP to notice, "Hey, you
just tried to send 5000 emails in the space of 2 minutes", if their
mail servers are in the message path.  And many ISPs are doing stuff
like POP-before-SMTP instead of authentication.

>However, even with authentication, if a system is zombied, probably
>would not take much for authentication credentials to be stolen by
>the malware and used for sending out spam.

It doesn't seem like they're doing that just yet, but of course it's
a continual arms race.


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