On Wed, 17 Dec 2003, Markus Stumpf wrote:
On Sun, Dec 14, 2003 at 11:13:03AM -0500, Daniel Feenberg wrote:
Perhaps you are confused by lax terminology. When anti-spammers speak of
filtering port 25, they mean packets destined to port 25 on the remote
system. That is the only port that accepts mail from strangers on most
systems.
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.
Port 25 blocking rendered useless.
Useless is perhaps too strong a word.
If some MTA operators wish to receive mail from blocked systems, that is
of course within their ability, and I don't think anyone wants to restrict
that. Most systems accepting mail on ports other than 25 use some form of
authentication. The problem solved by blocking outbound port 25 is that is
for ISPs that wish to reduce compliants about spam emmisions. Any system
receiving unauthenticated mail on another port, is unlikely to complain to
the source ISP.
Daniel Feenberg
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