Outlook sending attachments as winmail.dat

Question

We have a customer who can only receive plain text emails, i have change the settings in outlook and email are sent ok, but if we add an attachment they receive it as a winmail.dat file.

I have changed the registry keys, cleared the cache, recreated the profile and ran the fix it tool.

The email is definitely being sent as plan text by the attachment shows as, Content-Type: application/ms-tnef; name="winmail.dat"

Answer 1

You can follow this guide from Microsoft:
How to Prevent the Winmail.dat File from Being Sent to Internet Users

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If you have control over the Exchange server you need to change
Send Microsoft Exchange Rich Text and set it to Never:

• Open the Internet Mail Connector-Properties page.
• Click the General-tab.
• The Send Microsoft Exchange Rich Text list box controls the sending of rich-text data.
  Set this value to Never.

If you don't have control over your Exchange server you could try the following:

• You need to add the recipient to you address book.
• There you should be able to clear the checkbox for
  Always Send To This Recipient In Microsoft Exchange Rich-Text Format

If this still does not work there are some other methods you could try in the link above. Some of these options also depend on the version of Exchange (so if they don't work we need more detail to resolve the issue).

Another good resource to resolving the sending of winmail.dat is here.

Answer 2

If you have an Exchange Server 2013, you can also disable winmail.dat filename generation:

Get-RemoteDomain | Set-RemoteDomain -TNEFEnabled $False

Here is an example:

Exchange Server 2013: Ficheros adjuntos winmail.dat

It's in Spanish, but with screenshoots, it's easy to understand.