Core Issue
In the Cisco Unity 4.2 with Microsoft Exchange 2000 after an Internet subscriber is set up, the voice mail messages are sent to that subscriber with a DAT extension (winmail.dat) instead of a WAV extension.
Resolution
The DAT attachment is a product of the Exchange Simple Mail Transfer Protocol (SMTP) settings. Microsoft has a proprietary encoding method for attachments called Transport Neutral Encapsulation Format (TNEF). Only some clients can handle it, such as Microsoft Outlook or Microsoft Hotmail, but most others cannot, which includes Outlook Express. If the client can not handle the encoding method used, attachments appear as DAT.
In order to resolve this issue, force Exchange to use Multipurpose Internet Mail Extensions (MIME), a standard that is supported across all clients, and everything appears as WAV.
In order to force Exchange to use MIME, complete these steps:
Open Active Directory Users and Computers and look for the particular Internet subscriber.
Note: AD shows it as a Contact.
Right-click the subscriber, and choose Properties.
Click the E-mail Addresses tab.
Select the SMTP address, and click Edit.
Click the Advanced tab, and enable the Override Internet Mail Service setting for this recipient. The MIME message format is then selected.
Click Apply and OK in order to save the change.