smtp;550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

Question

I'm running Windows server 2008 R2 but am getting smtp mail rejected from a few domains.

To test it I'm dropping a text file into C:\inetpub\mailroot\Pickup directory, with something like this:

From: [email protected]
To: [email protected]
Subject: testing

This is a test

It will send to some domains, but some are returning:

Reporting-MTA: dns;DEDICAT-93I3U5A
Received-From-MTA: dns;DEDICAT-93I3U5A
Arrival-Date: Wed, 8 Aug 2012 12:50:58 +0100

Final-Recipient: rfc822;[email protected]
Action: failed
Status: 5.5.0
Diagnostic-Code: smtp;550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

I understand this could be something to do with the smtp setup on the server (IIS 7.5). Can anybody give me some advice as to where to start please?

Thanks,

Andy.

Answer 1

Some SMTP servers require you to send a valid host name with the HELO command that also is the same as the reverse DNS of the IP address the request originates from.

You can configure the host name the IIS SMTP Server uses through the old IIS6 Management Console. To do so, select the SMTP Server, right click and select Properties, go to the tab Delivery and then click on the button Advanced.

The reverse DNS for your IP address is usually controlled by your ISP.

Answer 2

FWIW, I had the same problem using hMailServer, and found the configuration instructions here. For the benefit of other hMailServer users, here's the field you need to set: