Error: The remote server returned an error: (400) Bad Request.
Posted by Daniel Weuthen on 28 Nov 2012 20:00

Problem: Windows authentication fails with error message The remote server returned an error: (400) Bad Request. although Standard-Authentication is working properly for that users.

Solution: If the Windows-User is member of many Active Directory groups, his Kerberos Security-Token becomes bigger than supported by the HTTP server (http.sys) default settings under Windows 2003.

The following registry keys under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters on the MailStore Server machine require adjustment:

  • MaxFieldLength
    Default value: 16384
    Valid value range: 64 - 65534 (64k - 2) bytes
    Registry key function: Sets an upper limit for each header. See MaxRequestBytes. This limit translates to approximately 32k characters for a URL.
  • MaxRequestBytes
    Default value: 16384
    Valid value range: 256 - 16777216 (16MB) bytes
    Registry key function: Determines the upper limit for the total size of the Request line and the headers. Its default setting is 16KB. If this value is lower than MaxFieldLength, the MaxFieldLength value is adjusted.

Please visit for more important information about changing http.sys related registry keys.

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