Outgoing SMTP Servers

Mark Andrews marka at isc.org
Wed Oct 26 22:11:41 UTC 2011

In message <op.v3y8xvo6tfhldh at rbeam.xactional.com>, "Ricky Beam" writes:
> On Tue, 25 Oct 2011 15:52:46 -0400, Alex Harrowell <a.harrowell at gmail.com>  
> wrote:>
> > Why do they do that?
> You'd have to ask them.  Or more accurately, you'd need to ask their  
> system integrator -- I've never seen an "in house" network run like that.  
> (and for the record, they were charging for that shitty network access.)
> Bottom line: Blocking port 25 (smtp) is undesirable, but necessary for a  
> modern consumer internet. (Translation: It f'ing works.) This is the ISP  
> saying, "You aren't a mail *server*."  

MTA == Mail Transfer Agent.  You don't have to be a *server* to be
a MTA.  Blocking SMTP also prevents your customers running encrypted
mail sessions to prevent nosy ISP's and others looking at what they
are sending.  With DNSSEC now being deployed and DANE being
standardised, running a SMTP session with STARTTLS is being a

Now most people don't care about this but you shouldn't have to get
a business grade service just to have secure email sessions and if
you want to run a SMTP server to do that you are not changing the
amount of traffic going over the connection so why the hell should
a ISP care.  IMAP, POP, SMTP all have about the same overhead for
inbound email.

> MUA's (mail clients) should only be  
> connecting to specified MSA's or MTA's (mail *servers*).  They should  
> never be connecting to random MTA's (presumably for direct delivery, which  
> is the job of an MTA not MUA.) The only people who can effectively police  
> this is the ISP.

Total utter BS.

> Individual mail server admins and RBL maintainers can  
> only guess and be reactionary, which is often wrong, still lets spam  
> through, and becomes stale rather quickly.
> --Ricky
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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