After Exchange 2010/2013 mailbox creation the task 'Initialize mailbox with E-Mail Address' fails with the following error message:
The underlying connection was closed: The connection was closed unexpectedly.
More detailed diagnostics is provided in the example below:
Last execution output: Provisioning request failed. Error in 'SW Managed Exchange.InitMailbox'. Exception calling "GetResponse" with "0" argument(s): "The underlying connection was closed: The connection was closed unexpectedly." Error position: At C:\Program Files\Parallels\Windows Provisioning Engine\Providers\SW Managed Exchange\InitMailbox.ps1:79 char:34 + $response = $request.GetResponse <<<< () Type: Parallels.Wpe.PowerShell.PowerShellException.
During a mailbox initialization connection to the Outlook Web Access service (OWA) is being established. In case the Microsoft Exchange Forms-Based Authentication service is stopped at the corresponding Client Access Server (CAS) OWA authentication does not work and task fails with the above mentioned error.
Find the OWA URL in the corresponding part of the wpe.log at the Windows Provisioning Engine (WPE) host. The default location of the WPE log is C:\Program Files\Parallels\Windows Provisioning Engine\Logs.
Try to login to OWA using the found URL. In case you deal with this particular issue you will meet the 'HTTP Error 500' after entering login/password.
Login to the server where OWA website resides and check status of the Microsoft Exchange Forms-Based Authentication service using the Services MMC snap-in. Start the service if it is stopped.
Check connection to OWA again and in case of successful login restart the failed task in the POA Task Manager.
The following Microsoft article provides more details about the issue with HTTP Error 500 on OWA authentication: http://blogs.technet.com/b/sbs/archive/2011/03/23/error-500-attempting-to-access-owa-on-sbs-2011-standard.aspx