Solution - IIS SMTP Service 5.5.2 rejected: need fully qualified hostname

We had a small problem today with a new site we were going live with. It was refusing to send emails in 90% of cases. Problems like these are always difficult to identify, but your first step is always to enable logging.

 1#Software: Microsoft Internet Information Services 7.0
 2#Version: 1.0
 3#Date: 2010-01-09 18:49:30
 4#Fields: c-ip cs-username s-sitename s-computername s-ip s-port cs-method cs-uri-query sc-win32-status cs-bytes cs-version cs(User-Agent) cs(Referer)
 5127.0.0.1 MYHOST-MYSERVER SMTPSVC1 MYHOST-MYSERVER 127.0.0.1 0 EHLO +ServerName 0 18 SMTP - -
 6127.0.0.1 MYHOST-MYSERVER SMTPSVC1 MYHOST-MYSERVER 127.0.0.1 0 MAIL +FROM:enquiries@company.com 0 47 SMTP - -
 7127.0.0.1 MYHOST-MYSERVER SMTPSVC1 MYHOST-MYSERVER 127.0.0.1 0 RCPT +TO:&lt;martin@hinshelwood.com&gt; 0 32 SMTP - -
 8127.0.0.1 MYHOST-MYSERVER SMTPSVC1 MYHOST-MYSERVER 127.0.0.1 0 DATA &lt;MYHOST-MYSERVERVoMDrx0000015e@MYHOST-MYSERVER&gt; 0 2560 SMTP - -
 9216.146.33.4 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 220+mx1.mailhop.org+ESMTP+MailHop+by+DynDNS.com 0 0 SMTP - -
10216.146.33.4 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 EHLO MYHOST-MYSERVER 0 0 SMTP - -
11216.146.33.4 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 250-mx1.mailhop.org 0 0 SMTP - -
12216.146.33.4 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 MAIL FROM:&lt;enquiries@company.com&gt;+SIZE=2884 0 0 SMTP - -
13216.146.33.4 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 250+2.1.0+Ok 0 0 SMTP - -
14216.146.33.4 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 RCPT TO:&lt;martin@hinshelwood.com&gt; 0 0 SMTP - -
15216.146.33.4 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 504+5.5.2+&lt;MYHOST-MYSERVER&gt;:+Helo+command+rejected:+need+fully-qualified+hostname 0 0 SMTP - -
16216.146.33.4 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 RSET - 0 0 SMTP - -
17216.146.33.3 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 220+mx1.mailhop.org+ESMTP+MailHop+by+DynDNS.com 0 0 SMTP - -
18216.146.33.3 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 EHLO MYHOST-MYSERVER 0 0 SMTP - -
19216.146.33.3 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 250-mx1.mailhop.org 0 0 SMTP - -
20216.146.33.3 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 MAIL FROM:&lt;enquiries@company.com&gt;+SIZE=2884 0 0 SMTP - -
21216.146.33.3 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 250+2.1.0+Ok 0 0 SMTP - -
22216.146.33.3 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 RSET - 0 0 SMTP - -
23216.146.33.3 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 250+2.0.0+Ok 0 0 SMTP - -
24216.146.33.3 OutboundConnectionCommand SMTPSVC1 MYHOST-MYSERVER - 25 QUIT - 0 0 SMTP - -
25216.146.33.3 OutboundConnectionResponse SMTPSVC1 MYHOST-MYSERVER - 25 - 221+2.0.0+Bye 0 0 SMTP - -

Figure: The log shows the source of the problem.

“5.5.2 rejected: need fully qualified hostname” tends to be destination server specific and relates to the server name that the mail is sent from which is different from the email from name. Most mail servers will reject mail from a name that they cannot lookup in DNS as an anti-spam measure.

To fix:

I opened “Internet Information Services (IIS) 6.0 Manager” on the server.
Expanded and then right click on “[SMTP Virtual Server #1]” and select “Properties”
Select the “Delivery” Tab and then “Advanced”
Enter “company.com” in the “fully-qualified domain name” field.
Click “ok” and then “ok” to save the changes

You should now be able to send emails from your site without any problems.

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