Outgoing SMTP Servers

Brian Johnson bjohnson at drtel.com
Thu Oct 27 13:53:34 UTC 2011

I find that large network providers have less issues with this issue.

As a small regional provider, implementing a "sane" port 25 filter has saved us a lot of money and customer headaches over the years. Our costs would be much higher if we could not save labor hours by implementing this. Possibly making service costs even more prohibitive. Pre implementation of these filters we had lower customer satisfaction, and were contemplating hiring more people to handle the labor load, due to UCE issues.

It is interesting that some people who fully understand that the Internet is composed of many networks run by people with different interests can say what is best for the Internet as a whole. How my organization (or yours or anybody else's) runs our network, is between us and our paying users.

But this thread has been interesting to follow. :)

 - Brian J.

>-----Original Message-----
>From: Owen DeLong [mailto:owen at delong.com]
>Sent: Wednesday, October 26, 2011 11:42 PM
>To: Scott Howard
>Cc: nanog at nanog.org
>Subject: Re: Outgoing SMTP Servers
>On Oct 26, 2011, at 8:07 PM, Scott Howard wrote:
>> On Tue, Oct 25, 2011 at 2:49 AM, Owen DeLong <owen at delong.com>
>> Interesting... Most people I know run the same policy on 25 and 587 these
>> days...
>> to-local-domain, no auth needed.
>> relay, auth needed.
>> auth required == TLS required.
>> Anything else on either port seems not best practice to me.
>> RFC 5068 covers the best practice, and it's not what you've got above.
>> Allowing unauthenticated inbound mail on port 587 defeats the entire
>purpose of blocking port 25 - the front door is now closed to spammers, but
>you've left the back door open! (Security through obscurity saves you here in
>that spammers rarely use port 587 - yet).  There isn't a single situations where
>you should be expecting an unauthenticated inbound message on the
>'Submission' port (is, 587)
>I still believe that that RFC is not correct. That blocking port 25 has too much
>collateral damage
>and is not a best practice.
>As such, you are correct, I am not following RFC 5068. A certain amount of
>spam does hit my
>system, but, the hosts that deliver it are identified and blocked reasonably
>> As much as some ISPs still resist blocking port 25 for residential customers, it
>does have a major impact on the volume of spam leaving your network.  I've
>worked with numerous ISPs as they have gone through the process of
>blocking port 25 outbound. In every case the number of end-user complaints
>has been low enough to be basically considered background noise, but the
>benefits have been significant - including one ISP who removed not only
>themselves but also their entire country from most of the 'Top 10 Spammers'
>list when they did it!
>Blocking outbound port 25 would not reduce the already infinitesimal volume
>of spam leaving my network in the least. It would, however, block a lot of
>legitimate traffic.
>No thanks.

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