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“The Server Is Unavailable” for a Single Exchange 2010 User

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Description of the Problem

You have one user on your Microsoft Exchange 2010 server who cannot open Outlook. When attempting to start Outlook, this user receives the message "The server is unavailable", with the options Work Offline, Retry, and Cancel. The user receives the same message regardless of which computer he or she tries to use. Other users can open Outlook without problems, even on the same computer as the user having the problem.

The affected user can log onto his or her Exchange account via Outlook Web Access.

If you check the Exchange server's application log, you observe the following error. The affected user's logon ID appears in the message:

Event 2915, MSExchangeADAccess
Process Microsoft.Exchange.AddressBook.Service.exe (PID=3960). User 'Sid~[DOMAIN]\[user]~RCA~false' has gone over budget '[n]' times for component 'RCA' within a one minute period. Info: 'Policy:DefaultThrottlingPolicy_b27689f1-3697-4b5c-89c7-9c82c5b31c9a, Parts:MaxConcurrency:128;'. Threshold value: '100'.


The user has exceeded a throttling limit. This means that the user's e-mail account is making too many concurrent connections to the Exchange 2010 server. Common causes of multiple concurrent connections include:

  • the user's mailbox or calendar are open on more than one computer
  • the user has numerous shared calendars or delegate mailboxes open
  • the user's account is synchronized with a mobile phone
  • the user's account is being used as a service account (unlikely, but possible)

You can view the user's connections to the server by running the following command in the Exchange Management Shell:

Get-LogonStatistics <UserID> | Fl ApplicationId

Each line of the output that reads "Client=MSExchangeRPC" represents a connection to the Exchange server.

You can also view the server's throttling policies:

Get-ThrottlingPolicy | Fl Name,RCA*

Unless it has been modified, the default throttling policy allows a maximum of 20 concurrent connections.

Outlook Web Access connections do not count toward this policy.


First, you may want to simply close all of the user's connections to find out whether the problem persists. This involves turniing MAPI access off, then back on. To do so from the Exchange Management Shell:

Set-CASMailbox -Identity <UserID> -MAPIEnabled $false
Set-CASMailbox -Identity <UserID> -MAPIEnabled $true

(Alternatively, you can open the user's mailbox in the Exchange Management Console and select the Mailbox Features tab. Highlight MAPI, then choose Disable and Apply. Then choose Enable and OK.)

If this procedure allows the user to open Outlook again, you can check to see how many shared calendars and delegate mailboxes he or she has open. There may be some connections that are not needed. You can also run the Get-LogonStatistics command again to see how many concurrent connections the user is now using.

If the issue recurs with the same user and you determine that he or she needs a higher limit, you can create a new throttling policy and assign the user to it. (You could also change the limit on the default policy, but you shouldn't.) Run the following commands in the Exchange Management Shell:

New-ThrottlingPolicy -name <Name>
Set-ThrottlingPolicy -Identity <Name> -RCAMaxConcurrency <Value>
  (You will want to specify a value greather than 20, or $null for no limit.)
Set-Mailbox -Identity <UserID> -ThrottlingPolicy <Name>


New-ThrottlingPolicy -name PowerUser
Set-ThrottlingPolicy -Identity PowerUser -RCAMaxConcurrency 40
Set-Mailbox -Identity JSmith -ThrottlingPolicy PowerUser

Once you have the user assigned to your new policy, he or she should be able to connect to Outlook.

David Carson
Posted on August 11, 2011
© Copyright Kinetic Computer Services

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