Summary

Outlook is a very common email client. If a sender of an email has TNEF enabled, the email sent (and received by the mail handler) will be TNEF-encoded

Quoting from Outlooks KB: https://support.microsoft.com/en-us/kb/290809

A TNEF-encoded message contains a plain text version of the message, and a binary attachment that "packages" various other parts of the original message. In most cases, the binary attachment is named Winmail.dat, and may include the following information:

• The formatted text version of the message (for example, font information and colors).
• OLE objects (for example, embedded pictures and embedded Microsoft Office documents).
• Special Outlook features (for example, custom forms, voting buttons, and meeting requests).
• Regular file attachments that were added to the original message.

The following is quoted from the same article above as well

Sending and Receiving Concerns
When an e-mail client that does not understand TNEF receives a message that contains TNEF information, the following are the three common results:

• The plain text version of the message is received and it contains an attachment named Winmail.dat. The Winmail.dat attachment does not contain any useful information when you open it because it is in the special TNEF format.
• Note: Some users have reported receiving a Win.dat attachment.

This is exactly what is happening to JSD mail handler at the moment. If a user sends an email with attachment using Outlook with TNEF enabled, the message is added to the ticket just fine, but Winmail.dat will be attached to the ticket, instead of the original intended attachment

Suggestion

Have the mail handler understand TNEF to decode Winmail.dat and attach the proper attachment