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MAPI Accelerator

The MAPI accelerator optimizes Microsoft Outlook Exchange e-mail traffic.  Exchange uses the EMSMDB protocol, which is layered on MS-RPC, which in turn uses either TCP or HTTP (unsupported) as the low level transport. 

The MAPI AO supports Microsoft Outlook 2000 through 2007 clients for both cached and noncached mode traffic.  Secure connections that use message authentication (signing) or encryption are not accelerated by the MAPI AO.  Such connections and connections from older clients are handed off to the generic AO for TFO optimizations.  Additionally, Outlook Web Access (OWA) and Exchange-Exchange connections are not supported. 

Note: Microsoft Outlook 2007 has encryption enabled by default.  You must disable encryption to benefit from the MAPI application accelerator.  In Outlook, choose Tools > E-mail Accounts, choose View or Change Existing E-mail Accounts, and then click Next.  Choose the Exchange account, and then click Change.  Click More Settings, and then click the Security tab.  Uncheck the Encrypt data between Microsoft Office Outlook and Microsoft Exchange Server check box, as shown in Figure 1. 

Alternatively, you can disable encryption for all users of an Exchange Server by using a Group Policy. 

Figure 1.  Disabling Encryption in Outlook 2007

In the following cases, the MAPI AO does not handle a connection:

Encrypted connection (handed off to the generic AO)

Unsupported client (handed off to the generic AO)

Unrecoverable parsing error.  All TCP connections between the client and server service are disconnected.  When the client reconnects, all connections are handed off to the generic AO. 

Client attempts to establish a new association group on the connection when the WAE is overloaded. 

Client establishes a connection when the WAE is overloaded and MAPI reserved connection resources are not available. 

The Outlook client and server interact in a session over a group of TCP connections called an association group.  Within an association group, object accesses can span across any connection and connections are dynamically created and released as needed.  A client can have more than one association group open at the same time to different servers or the same server. ( Public folders are deployed on different servers from the mail store.) 

It is essential that all MAPI connections within an association group go through the same pair of WAEs in the branch and data center.  If some connections within an association group do not go through the MAPI AO on these WAEs, the MAPI AO would not see the transactions performed on those connections and the connections are said to "escape" the association group.  For this reason, the MAPI AO should not be deployed on serially clustered inline WAEs that form a high availability group. 

The symptoms of MAPI connections that escape their WAE association group are Outlook error symptoms such as duplicate messages or Outlook stops responding. 

During a TFO overload condition, new connections for an existing association group would be passed through and escape the MAPI AO, so the MAPI AO reserves a number of connection resources in advance to minimize the impact of an overload condition.  For more details about reserved MAPI connections and their impact on device overload, see the section "MAPI Application Accelerator Reserved Connections Impact on Overload" in the Troubleshooting Overload Conditions article. 

Verify the general AO configuration and status with the show accelerator and show license commands, as described in the Troubleshooting Application Acceleration article.  The Enterprise license is required for MAPI accelerator operation and the EPM application accelerator must be enabled. 

Next, verify the status specific to the MAPI AO by using the show accelerator mapi command, as shown in Figure 2.  You want to see that the MAPI AO is Enabled, Running, and Registered, and that the connection limit is displayed.  If the Config State is Enabled but the Operational State is Shutdown, it indicates a licensing problem. 

Figure 2.  Verifying the MAPI Accelerator Status

Use the show statistics accelerator epm command to verify that the EPM AO is functional.  Check that the Total Handled Connections, Total Requests Successfully Parsed, and Total Responses Successfully Parsed counters increase when a client is started. 

Use the show running-config command to verify that the MAPI and EPM traffic policies are properly configured.  You want to see accelerate mapi for the Email-and-Messaging application action and you want to see the MS-EndPortMapper classifier and traffic policy defined, as follows:

Use the show policy-engine application dynamic command to verify that dynamic match rules exist, as follows:

Look for a rule with User ID: EPM and Map Name: uuida4f1db00-ca47-1067-b31f-00dd010662da. 

The Flows field indicates the total number of active connections to the Exchange service. 

For each MAPI client you should see a separate entry with the User ID: MAPI. 

Use the show statistics connection optimized mapi command to check that the WAAS device is establishing optimized MAPI connections.  Verify that "M" appears in the Accel column for MAPI connections, which indicates that the MAPI AO was used, as follows:

Note: In version 4.1.5, the Current Reserved Flows counter was added in the output.  This counter refers to the number of reserved MAPI connection resources on the WAE that are currently unused but set aside for future MAPI connections.  For more details about reserved MAPI connections and their impact on device overload, see the section "MAPI Application Accelerator Reserved Connections Impact on Overload" in the Troubleshooting Overload Conditions article. 

If you observe connections with "TGDL" in the Accel column, these connections were pushed down to the generic AO and optimized with transport optimizations only.  If these are connections that you expected to be handled by the MAPI AO, it may be because they are encrypted MAPI connections.  To check on the number of encrypted MAPI connections that have been requested, use the show statistics accelerator mapi command as follows: