Mail Submission Protocol

Mike Walter mwalter at
Wed Apr 21 09:05:34 CDT 2010

We have had very good luck with using port 587 and requiring the users
to authenticate to send email from outside our network. 

Inside customers, we have not changed to force port 587 and
authentication for email clients, but the topic has come up in
discussions.  This won't of course, stop spammers if they are hijacking
the users local email client settings.


-----Original Message-----
From: Claudio Lapidus [mailto:clapidus at] 
Sent: Wednesday, April 21, 2010 9:49 AM
To: nanog at
Subject: Mail Submission Protocol

Hello all,

At our ISP operation, we are seeing increasing levels of traffic in our
outgoing MTA's, presumably due to spammers abusing some of our
accounts. In fact, we are seeing connections from IPs outside of our
as many as ten times of that from inside IPs. Probably all of our
are travelling abroad and sending back a lot of postcards, but just in
case... ;-)

So we are considering ways to further filter this traffic. We are
implementation of MSA through port 587. However, we never did this and
like to know of others more knowledgeable of their experiences. The
is what best practices and stories do you guys have to share in this
Also please let me know if you need additional detail.

thanks in advance,

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