From: Bill Cole (postfixlists-070913billmail.scconsult.com)
Date: Mon Oct 08 2007 - 16:31:57 CDT

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At 2:03 PM -0500 10/8/07, Nishant Limbachia wrote:
>Hi list members,
>
>I have trouble sending emails out of my server. I've configured the
>server and everything works except sending emails via my ISP.
>Unfortunately my ISP blocks port 25 so I have to use their servers for
>now. ISP recommends using port 587.

I think you may be misinterpreting their recommendations. That's
understandable, given that there is a misleading statement on this
issue on one of the key pages in their support site.

>I'm a newbie learning postfix. Sending mails within the network or
>receiving them from
>outside world works perfect. Can anyone of you give a hint on solving
>this? I am using postfix 2.4.5. I'm running firewall on the machine
>(dynamic IP) and machine is also behind a router. Both the machine and
>router has port 25 and 587 open (input and output).
>
>Thanks,
>
>Note: I am particularly intrigued by the "relay=none" in the postfix logs for
>outgoing mails.
>
>Here's how I've setup relaying via my ISP
>
># /etc/postfix/main.cf
>relayhost = [ <http://smtp.att.yahoo.com/>smtp.att.yahoo.com]:587

That host is the one provided for AT&T's DSL customers, but the
documentation I see DOES NOT specify using port 587.
http://helpme.att.net/article.php?item=10918 says to use port 465,
which is Microsoft's standard-by-fiat port for SMTP over SSL. I don't
believe that Postfix will (or should) do that. If you feel like
sending your authentication info in the clear over an unencrypted
channel for the privilege of using a rather unreliable relay system,
you can use port 25 on smtp.att.yahoo.com but you will need to adapt
your SASL client config to accommodate the fact that the name is
resolved via CNAME's to a name under akadns.net in what looks like a
scheme to do load balancing via DNS utilizing short TTL's.

Alternatively, AT&T will unblock port 25 to the rest of the world for
you on request. See http://helpme.att.net/article.php?item=4640 and
enjoy the irony that on that page they urge the use of port 587 for
submission even though they don't support it themselves.

--
Bill Cole
billscconsult.com

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