XADM: Description of the MAPI Client Connection Polling of an Exchange Server (813112)

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When you open a message, save it, copy it to another folder, or delete it, the MAPI client communicates with a message store service. The Emsmdb32.dll component is involved if you are working with items that are stored on an Exchange server. Emsmdb32.dll is part of the Exchange transport service and provides the services that are required for accessing public folders and your mailbox. Emsmdb32.dll is also involved if you are working with an offline folder store.

When the MAPI client is connected to an Exchange server, the Emsmdb32.dll component performs an hourly remote procedure call (RPC) keep-alive call to the Exchange server to make sure that the connection is still established. This hourly check is performed by each connected MAPI client and is controlled by the PR_PROFILE_RECONNECT_INTERVAL function. For example, if you are monitoring a network that contains 100 mailboxes on one server and 100 mailboxes on another server, you see 200 Transport Control Protocol (TCP) connections that are trying to obtain a response from the Exchange servers each hour. The number of connections to the Exchange server is limited only by the ability of the server or network to handle the network traffic.

The following issues that change this polling interval may occur:

• An unsuccessful RPC connection:
  If an hourly polling connection attempt is unsuccessful, the connection is retried in 5 minutes. If this connection is successful, the MAPI client returns to the default hourly check with the server.
• An unsuccessful connection retry:
  In some cases, the MAPI client cannot establish a connection with the Exchange server when it retries an unsuccessful polling connection. In this case, it waits for 10 seconds, and then retries the connection on the next "reconnect" interval after 5 minutes.
• The hourly connection polling stops:
  If no connection errors or timeouts occur between the client and the server, the hourly polling is not performed.

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