Question : Relay Denied errors more abundant lately.

I've been seeing an increased number of "Relaying denied" NDR's coming into my mail server these past week weeks.  I've checked and double checked with my ISP to ensure my DNS records are configured properly and they swear up and down they are.  I have been questioning them about Reverse DNS and they tell me they "have many customers using mail servers that are set up the same way we are"...

Most of our mail is fine, but maybe 1-2% of it comes back with a relay denied NDR of some sort.. usually stating "Authenitcation" issues.  Our setup uses Exchange 2003 and local Outlook 2003 from our office where the mail server is located.

Here's an example from my log files; can anyone make sense if it?

207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:58:59, SMTPSVC1, SERVER, -, 297, 0, 78, 0, 0, -, -, 220 ns3.quik.com ESMTP Sendmail 8.13.1/8.13.1; Thu, 25 Oct 2007 12:00:01 -0700,
207.38.29.36, OutboundConnectionCommand, 10/25/2007, 11:58:59, SMTPSVC1, SERVER, -, 297, 0, 4, 0, 0, EHLO, -, server.tacs.org,
207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:58:59, SMTPSVC1, SERVER, -, 375, 0, 92, 0, 0, -, -, 250-ns3.quik.com Hello 69-30-69-184.dq1mn.easystreet.com [69.30.69.184], pleased to meet you,
207.38.29.36, OutboundConnectionCommand, 10/25/2007, 11:58:59, SMTPSVC1, SERVER, -, 375, 0, 4, 0, 0, MAIL, -, FROM:,
207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2563, 0, 38, 0, 0, -, -, 250 2.1.0 ... Sender ok,
207.38.29.36, OutboundConnectionCommand, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2563, 0, 4, 0, 0, RCPT, -, TO: NOTIFY=NEVER,
207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2657, 0, 84, 0, 0, -, -, 550 5.7.1 ... Relaying denied. Proper authentication required.,
207.38.29.36, OutboundConnectionCommand, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2657, 0, 4, 0, 0, RSET, -, -,
207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2719, 0, 21, 0, 0, -, -, 250 2.0.0 Reset state,
207.38.29.36, OutboundConnectionCommand, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2719, 0, 4, 0, 0, QUIT, -, -,
207.38.29.36, OutboundConnectionResponse, 10/25/2007, 11:59:02, SMTPSVC1, SERVER, -, 2797, 0, 41, 0, 0, -, -, 221 2.0.0 ns3.quik.com closing connection,

Answer : Relay Denied errors more abundant lately.

Call your ISP, and then ask for someone who understands how the internet works.
Reverse DNS records are NOT optional. The fact that no one else complains is not a sign that everything else is working correctly.

Point the ISP at AOL's postmaster site, specifically on this page where it says that the server must have a valid DNS record. http://postmaster.aol.com/guidelines/bestprac.html

This sounds like a lazy ISP, or first line support trying to get rid of you.

Or put your domain in to dnsreport.com and see what errors it flags in the mail server section.

While the reverse DNS is not correct, I would not expect them to generate those sorts of warnings.

The last one means what it says - User Unknown.
The Proper Authentication required is usually an indication that an internal SMTP server has been put in to the MX records in error or a server mis-configured.

I would also state that I don't receive a copy of the NDRs on any of the servers that I manage. I have much better things to do with my time than worry about those. If the users are getting errors they will soon complain - most of them are typos anyway.

Simon.

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