Receiving email attachments as winmail.dat

Whenever I receive emails from one particular email domain (there are several people that regularly send me emails from this domain), the attachments come through as a single winmail.dat file rather than the actual PDF, XLS, etc, files.

This happens on all devices (MacBook, iPhone, iPad, and my colleagues Samsung and Laptop) and mail software (currently using Outlook 2013, but have tried Apple Mail and same issue).

The only way to retrieve the attachments is to login to the online server/host and then either download from there or forward the email to myself, in which case they come through fine.

Emails with attachments sent from any other domain are fine, just this particular one is having the issue.

Please help!!!!
 
This is a problem created by Outlook users. If I recall correctly, have the sender set your preferred email as TEXT, not HTML.
 
Thanks for the reply!

We've actually tried the method of having the sender change the email format and this still hasn't worked. Also having googled the issue in the past, this seems to be the fix for the majority of cases but hasn't worked for us!

It's just interesting that it has never been an issue from other senders using Outlook - it only occurs from this one particular email client. Someone mentioned it could have something to do with the difference in security levels between the sender and our email server, but not being someone who is overly technically proficient, I wasn't sure if this was a possibility?
 
It is absolutely a SENDER side problem, as email readers respond to, and do net set the file name extension.
 
To prevent Outlook from attaching winmail.dat when you send an email:
  1. Click File in Outlook.
  2. Select Options.
  3. Go to the Mail category.
  4. Make sure HTML or Plain Text is selected for Compose messages in this format: under Compose messages.
 
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