Hi Scott,
Thanks for the clarifications. So you're saying 587 should not be used for
MUA -> MTA traffic? So there's no need or intention for users to switch to
587 in the their mail client?
If we need to listen on both 25 and 587, does IMail support that? I haven't
seen anything that allowed IMail to listen on multiple ports. Is that
something we would need to map in a router or firewall to satisfy the
requirements?
Darin.
----- Original Message -----
From: "R. Scott Perry" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, August 02, 2004 2:28 PM
Subject: Re: [IMail Forum] BellSouth now blocking port 25
>I wonder how long before ISPs start blocking 587. Certainly it doesn't
>take much for spammers to switch to 587 as well.
There is a reason why an RFC defined port 587 when port 25 already existed.
:)
Port 25 is used for any SMTP connections -- from MUA (mail client) to MTA
(mail server) and MTA to MTA. Many ISPs now block outgoing connection to
port 25 since their customers should not be sending out E-mail directly to
other mailservers (as that is how spammers operate), and it is impossible
to distinguish MUA->MTA traffic from MTA->MTA traffic.
However, port 587 traffic is *only* used for MTA->MTA traffic. For
example, if @example.com has an MX record pointing to a host that resovles
to 192.0.2.25, that IP is required to accept mail on port 25. If it also
accepts E-mail on port 587, it should only accept E-mail from authenticated
users. If it accepts E-mail from non-authenticated users (I haven't heard
of it happening yet), it will almost certainly get blacklisted. So ISPs
have no need to block port 587 traffic.
-Scott
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