Did you know ?

Have you ever received a winmail.dat file ?

This is a Windows issue… People who use windows use a non standard file format or their email servers are very old. To solve this issue you should educate the person who is sending the files not to us TNEF and send as a HTLM or plain text format. This issues is always caused by user who send in this way.

Another solution is for Mac users is to download a simple app either for your desktop or iPhone. You can use these links below 

http://www.joshjacob.com/mac-development/tnef.php

https://itunes.apple.com/us/app/tnefs-enough/id1059932557?ls=1&mt=8

Some Outlook features require TNEF encoding to be understood correctly by an Internet email recipient who also uses Outlook. For example, when you send a message that has Voting buttons to a recipient over the Internet, if TNEF is not enabled for that recipient, the Voting buttons are not received. Or, for sending messages that have regular file attachments, TNEF is not needed. If you are sending messages that have file attachments to a recipient who does not use Outlook or the Exchange Client, we recommend that you manually choose to use an email format which does not require TNEF (such as HTML or plain text). If a message is sent without TNEF, the recipient can view and save the attachments as expected.

For more information you can read Microsofts support pages here:

https://support.microsoft.com/en-in/help/290809/how-e-mail-message-formats-affect-internet-e-mail-messages-in-outlook