Symantec Mail Security for Microsoft Exchange (SMSMSE) cannot be installed in a 2008 domain when the installer returns the error "Failed to verify user has mailbox" with exit code 100 after entering credentials for the SMSMSE service account.
In the ExeMonadE2K10_E2K15.log (located in the temp directory) the following error is observed:
Windows PowerShell updated your execution policy successfully, but the setting is overridden by a policy defined at a more specific scope. Due to the override, your shell will retain its current effective execution policy of "<policy setting>". Type "Get-ExecutionPolicy -List" to view your execution policy settings. For more information, please see "Get-Help Set-ExecutionPolicy."
A group policy object (GPO) is preventing the SMSMSE installer from executing the PowerShell script necessary to determine whether the service account has a mailbox associated.
Configure the "Turn on Script Execution" GPO to allow SMSMSE powershell scripts to run:
To configure the GPO: