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Re: [Asrg] 6. Proposals: MTA MARK vs port 25 filtering?

2004-01-16 19:50:06
If you start to block port 25 outgoing people will start to make wide
use of SRV records, because a lot of receiving MTAs will /want/ to 
talk to users behind port 25 blocked networks.
With SRV records you don't need well-known ports any longer, but you
specify the port your SMTP speaking MTA is listening on in the SRV
record itself.

I don't know of anyone who has much interest in getting SMTP
connections from random PPP and DHCP users.  I know that to a very
close approximation, that mail is 100% spam and viruses.

On the other hand, I am quite happy for my users, all of whom use
other ISPs to connect to the net, to use SMTP AUTH to prove who they
are, and then send mail to anyone they want.  That's known as SUBMIT,
and the standard port is 587.  I should publish a few SRV records in
case anyone goes looking for them.

Port 25 blocking rendered useless.

Not at all, it does exactly what it's supposed to. It forces mail to
strangers to be passed through the ISP's MTA where there's some chance
of detecting spam on the way out.

Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
http://www.taugh.com

-- 
John R. Levine, IECC, POB 727, Trumansburg NY 14886 +1 607 330 5711
johnl(_at_)iecc(_dot_)com, Village Trustee and Sewer Commissioner, 
http://iecc.com/johnl, 
Member, Provisional board, Coalition Against Unsolicited Commercial E-mail

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