This issue may go out by itself. But if the user is still experiencing the issue, try to close the IP connections, and investigate what on his desktop (or on other desktops if he has multiple opened connections) can generate too much MAPI connections.
Usually, it can be caused by VPN connections closing and users re-opening them. When a VPN connection closes, the MAPI session to an Exchange Server is not released. Then re-establighing the VPN then the MAPI connection just add more MAPI connections
It can also be caused by an external MAPI based device such as Blackberry or application such as scripts or third-party mail applications.
1- First, checkout the IP address of UserAlias listed in the Distinguished Name of the event :
Get-LogonStatistics UserAlias | ft Name,ClientIPAddress
Note: if the client is not more connected to the Exchange server or the MAPI sessions finally closed by themselves, the ClientIPAddress property will be blank
2- Using a tool like TCPView (http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx), close the connections from your Exchange server that refer to the ClientIPAddress you just get with the PowerShell command in Step-1
Again, forcing TCP connections without knowing the cause of what caused them is not very clever. The MAPI connections exhaustion may come back.
Check with the user’s devices and applications he is using to connect to the Exchange server as you may be able to solution the issue for a broader number of users.