Outgoing SMTP Servers

Owen DeLong owen at delong.com
Wed Oct 26 23:41:44 CDT 2011


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> wrote:
> 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 quickly.

> 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.

Owen



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