North American Network Operators Group

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Re: Why do so few mail providers support Port 587?

  • From: Adrian Chadd
  • Date: Fri Feb 25 11:54:51 2005

On Fri, Feb 25, 2005, Nils Ketelsen wrote:

> It's so funny. On this list many argued Port 25 outgoing must
> be blocked only to notice, that users actually seem to need it to
> send mail. Now we must configure our mailservers to listen on 587 to
> circumvent these filters, that were stupid in the first place.
> Now to my prophecy mode: Spammers will start using 587 to spam, which we
> then also all block outgoing, notice again that customers still want to
> send mail and open another port ... 652 maybe. But this in a
> "while (true)" loop until we run out of ports.

kind of. the reason port 25 is filtered is because spammers were
making direct connections from (host) to (domain MX). This isn't
distiguishable from normal SMTP except by things like SPF which
authenticate the /sender/ host.

port 587 is different - the spammers can use it but the spam now
passes through your ISP configured mailserver. much like how spammers
are sometimes poking the registry/configuration to use configured
MTAs since direct connection to domain MX servers isn't always working.
so yes, it'll eventually be used by spammers but, by its very nature,
the spam source will be easily identified and throttled at their end.


Adrian Chadd			"You don't have a TV? Then what's
<[email protected]>	    all your furniture pointing at?"