Helo command rejected: need fully-qualified hostname when sending emails

Simple tip this afternoon. You may have got the following error when sending emails through ASP.Net’s built in mail server before:

From: postmaster@YourWebserversName [mailto:postmaster@YourWebserversName] Sent: 25 June 2010 13:22 To: sender@sendingdomainname.com Subject: Delivery Status Notification (Failure) This is an automatically generated Delivery Status Notification. Delivery to the following recipients failed. recipient@recievingdomainname.com Reporting-MTA: dns;YourWebserversName Received-From-MTA: dns;YourWebserversName Arrival-Date: Fri, 25 Jun 2010 13:21:30 +0100 Final-Recipient: rfc822;recipient@recievingdomainname.com Action: failed Status: 5.5.0 Diagnostic-Code: smtp;504 <YourWebserversName>: Helo command rejected: need fully-qualified hostname

The fix is easy:

1. Open IIS
2. View the properties of you Default SMTP Virtual Server
3. Go to the “Delivery” tab
4. Click the “Advanced” button (in the bottom right corner)
5. Under “Fully-qualified domain name” enter a domain name that points to the server
6. Click Ok until you’re back to IIS