Saturday, June 6, 2009

Autodiscover Issue: 401 Unauthorized

Autodiscover was not working at a client, we were just getting a 401 Unauthorised error. I know for a fact authenticated users had NTFS read permissions of the autodiscover virtual directory so it was a weird issue. Here are the symptoms we were recieving:

When we log into the exchange server and go to the autodiscover website in internet explorer using localhost it works:

When you go to the proper address set by Set-ClientAccessServer -Identity CLIENTACCESSSERVER -AutoDiscoverServiceInternalUri domain.local you get the following error the same as powershell:

This is caused by the loopback check being enabled. To disable loopback perform the following action on the client access servers:

1.Click Start, click Run, type regedit, and then click OK.
2.In Registry Editor, locate and then click the following registry key:
3.Right-click Lsa, point to New, and then click DWORD Value.
4.Type DisableLoopbackCheck, and then press ENTER.
5.Right-click DisableLoopbackCheck, and then click Modify.
6.In the Value data box, type 1, and then click OK.
7.Quit Registry Editor, and then restart your computer.

Now when you test autodiscover settings everything will work:


  1. That worked really well - Thanks :)

  2. Great content Clint, this helped me out immensely!!

  3. Thanks A lot, you saved my ass ! :D

  4. Solved my problem perfectly. Thanks Clint!

  5. this happened only for extranal user right?

  6. Great ... tried and searched everywhere since yesterday but your solution fixed it. Thanks !

  7. Are there any implications or risks with disabling the Loopback check? What does the loopback check do?