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When a user who is not assigned a Session Initiation Protocol (SIP) account uses custom tabs in Microsoft Office Communicator 2007, Communicator 2007 passes a string that resembles the following to the tab URL:
Communicator 2007 appends the telephone number to the user name in the string. This action may cause issues for programs that service the tab URL.
To resolve this problem, download and then install the hotfix that is described in the following Microsoft Knowledge Base article:
943083 Description of the Communicator 2007 hotfix package: December 17, 2007
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
A new feature is included in the Communicator 2007 hotfix package that is dated December 17, 2007. This feature appends contact e-mail addresses to the user name. The new element mailto that is included in this Communicator 2007 hotfix package can be used to pass e-mail addresses for users who do not have an SIP account.