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BES 5 – Exchange connectivity issues via Load Balancer


BlackBerry Exchange Server (BES) 5 users experience intermittent issues with their devices. For example, they receive some emails promptly whereas others after a delay of a few minutes.

The following "Warning" (Event 20709) is seen in the Application Event Logs on the BES 5 Server:

Application Event Log Warning

The following error is seen in the BlackBerry Messaging Agent (MAGT) logs:

[40720] (11/14 00:03:57.796):{0x19E4} MAPI call failed. Error ‘Network problems are preventing connection to the Microsoft Exchange Server computer.’, LowLevelError 6, Component ‘Microsoft Exchange Server Information Store’, Context 1300

Background & Analysis:

  • We were failing over our BES 5 server from primary (site A) to standby (site B).
  • In site A, the BES 5 server connected directly to 1 Exchange CAS node, whereas in site B, the BES 5 server connected to an F5 load balancer which load balanced connections across 2 Exchange CAS nodes (redundancy).
  • Our Exchange Server was on Exchange 2010.
  • BES 5 communicates with Exchange via MAPI/RPC.



WORKAROUND: Configure BES 5 to communicate directly with an Exchange CAS node, bypassing the F5. Refer BlackBerry KB28704

Possible Solution: I haven’t tested this solution yet, but BlackBerry KB26490 describes a possible solution with a specific F5 configuration (iRules).

 NOTE: Using an F5 load balancer in front of Exchange CAS nodes requires an appropriate configuration of the F5. Refer this detailed F5 deployment guide.

(1) The solution above describes a successful problem-solving experience and may not be applicable to other problems with similar symptoms.

(2) Your rating of this post will be much appreciated as it gives me and others who read this article, an indication of whether this solution has worked for people other than me. Also, feel free to leave comments.


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