One of the many reasons why the “Test E-Mail AutoConfiguration” for AutoDiscover fails with “(0x800C8203)”

While troubleshooting a Tanjay issue a week ago, we noticed that AutoDiscover wasn’t working properly when we used Outlook 2007’s Test E-Mail AutoConfiguration feature (simply press and hold the CTRL key and left-click on your Outlook 2007 icon):

… as it would continually fail with:

Autodiscover to https://autodiscover.internalDomainName.com/autodiscover/autodiscover.xml FAILED (0x800C8203)

Before I continue, let me state that the domain names for the company were:

External: domain.com

Internal: inside.domain.com

What was strange was that if I run the test with the default E-Mail Address as: username@inside.domain.com, the autodiscover test would fail but if I removed the “inside” from the email address, it would pass.  After troubleshooting for an hour and running low on options, I went ahead and logged onto the Exchange 2007 server, navigated to the users window, opened up the user account I was testing with to check the email address and this is what I saw:

I know it’s not easy to see since I had to blank out a lot of the fields but what I saw was that the SMTP address listed in the SMTP section only had the public domain name listed and not the inside.domain.com.  This was more or less of a hunch that I had after running out of options so I went ahead and created a username@inside.domain.com email address.

Once I created the email address and tried running the Test E-Mail AutoConfiguration feature, the results came back as completed without errors.

I did a fair bit of research while troubleshooting this issue and did not find any posts that had this solution to fix the issue so I hope this will help anyone out there that may come across this issue.