How does Outlook know if the recipient cannot receive RTF messages

Question

I am suffering from the winmail.dat problem. I tried to fix the problem through making email senders. But no success.

In this "How to Prevent the Winmail.dat File from Being Sent to Internet Users" document, Microsoft says:

... Winmail.dat may be automatically added to the end of the message if the recipient's client cannot receive messages in Rich Text Format (RTF).

How does Outlook know if a recipient cannot receive RTF messages?

Answer 1

Outlook does not know if the recipient can accept Outlook Rich Text format. This Rich Text is not to be confused with Rich Text Format (.RTF), that you can save Word documents into. If the recipient's e-mail client can not process the Outlook Rich Text, it gets attached as a WinMail.dat attachment.

For best result, use Plain Text and HTML only.

Outlook Rich Text can be used if you only plan to send within your organization that uses Outlook as well, or the recipient has Outlook. If you do not know, use HTML or Plain Text.

This has been a problem for over 10 years using Microsoft Outlook and they've never bothered to address it.

Answer 2

Outlook doesn't know anything about the recipient's email client, and the receiving email client doesn't create the winmail.dat file. That Microsoft link is poorly worded, making it a bit confusing. The wording really means:

If the message contains formatting other than plain text content and/or has attachments, Winmail.dat will be automatically added to the end of the message in case the recipient's client cannot handle messages in Rich Text Format (RTF) the way Microsoft has implemented it.

Everything happens at the originating end. The winmail.dat file preserves the original content, but not in a way that the recipient can use natively.

The way Outlook stores RTF messages is to put everything into the winmail.dat file, and then produce a plain text version of the message for the message body. At the receiving end, most email clients (other than Outlook and a couple of others), simply ignore the winmail.dat file and just display the plain text content.

Some useful information on handling the winmail.dat file:

• How do I handle Microsoft Outlook winmail.dat
• TNEF This link includes links to many utilities for opening winmail.dat files
• Handling winmail.dat in Thunderbird This Mozilla link also includes links to a number of free utilities for opening winmail.dat files