My users receive winmail.dat attachments they can't open, or "application/ms-tnef" attachements.
- On-Premise Server + WebMail Installations: Version 6.0 > Current Version
- Webmail Only Installations: Version 6.0 > Current Version
Emails sent from Microsoft Outlook in Rich Text Format messages are sent as a bundled attachment called winmail.dat, using Transport Neutral Encapsulation Format.
If your server doesn't include support for these files you will see the winmail.dat attachments.
Adding support for TNEF files is fairly simple and just requires the installation of a package.