Hey Chong,
Since you are integrating with Unity w/ Exchange, please make sure that you are using the AD Password and not the PIN used to check the Voicemail through the Phone. If that still fails, please try the following command from the CLI
Open up command prompt from your pc and type the following
telnet 192.168.60.50 143
1 capability
2 login userid password
For the userid/password, use the credentials of the affected user.
->Now if you are not able to telnet to Port 143 on Exchange server, then that means that IMAP is not enabled.
->If when you type the command "1 capability" and get an output where you see LOGINDISABLED being listed among other things, that means that Exchange does not allow authentication over IMAP and/or secure authentication is enabled. There, we need to have Authentication over IMAP enabled
Let me know where it fails.
BR,
Jasmeet