Error: "Trying to connect to Microsoft Exchange Server" results in MAPI_E_LOGON_FAILED

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Article ID: 2019948 - View products that this article applies to.
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Outlook Dialogue box pop- up stating “Trying to Connect to Microsoft Exchange Server.”  You may get a MAPI_E_LOGON_FAILED


Windows Server 2008 GC’s have a limitation of 50 concurrent NSPI connections per user. 
Applications such as Outlook 2007, Blackberry Enterprise Server, or any application that will create multiple NSPI connections to a DC/GC can experience these symptoms.


  1. To Resolve this issue, modify the following registry entry. 
  2. Click Start, click Run, type regedit, and then click OK
  3. Locate and then click the following registry key:
  4. On the Edit menu, point to New, and then click Key.
  5. Type Parameters, and then press ENTER. 
  6. Click the Parameters key. 
  7. On the Edit menu, point to New, and then click DWORD Value
  8. Type NSPI max sessions per user, and then press ENTER. 
  9. Double-click NSPI max sessions per user, type the number of the NSPI connections required, and then click OK.

Note: There is no specific upper-limit to this setting beyond the limits that are imposed by it being a DWORD (that is, 0xffffffff or about 4 billion). Configuring the server in this manner will make it function similarly to Windows Server 2003 in terms of the maximum number of NSPI connections that are allowed per user.  This modification was made to Server 2008 to limit the ability of one user account depleting the resources of any particular DC.  Modifying this entry may cause performance issues on the DC as we create a new page in memory for each NSPI connection.

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Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use for other considerations.


Article ID: 2019948 - Last Review: February 26, 2010 - Revision: 1.0
  • Microsoft Exchange Server 2010 Enterprise
  • Microsoft Exchange Server 2010 Standard
  • Microsoft Exchange Server 2007 Enterprise Edition
  • Microsoft Exchange Server 2007 Standard Edition
  • Microsoft Exchange Server 2003 Standard Edition
  • Microsoft Exchange Server 2003 Enterprise Edition

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