RSSRecipients are receiving winmail.dat attachments
Non-Outlook users receive messages as plain text; formatting and attachments are in a winmail.dat file
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Converting to or from
Outlook or Exchange:
Messages and Calendar
or
Address books
There is a long standing "problem" between Outlook and Internet email - Outlook uses a proprietary email format that only Outlook and Exchange (and a few other clients, including gmail) can decipher. When the recipient doesn't use Outlook, they get plain text message and an attachment named winmail.dat (the attachment icon may be hidden by some clients, including OE and Windows Mail).
Any attachments included in the message are encased in the winmail.dat attachment.
Exchange administrators can disable RTF on messages sent to the Internet.
If you arrived on this page because you received a winmail.dat attachment and don't use Outlook, see the Tools below for utilities you can use to retrieve attachments from the winmail.dat file. Don't bother looking in winmail.dat files if you were not expecting an attachment (or if the message size indicates there is probably not an attachment). Or ask the Outlook user to resend the file, using plain text format.
What is RTF, TNEF and winmail.dat?
Outlook can
use a special method, technically referred to as Transport Neutral
Encapsulation Format (TNEF), to package information for sending messages. The use of TNEF is
affected by settings in Outlook that are referred to as Rich Text Format
(RTF). TNEF and RTF are not identical, but they are very similar.
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
it includes the following information (if included in the message):
Where to check for RTF settings in Outlook
When RTF is not working as expected (either all messages are RTF, or Meeting Requests and Voting are not working) there are several settings your need to check in Outlook. Note: Exchange server administrators can also control RTF to Internet addresses. If the administrator disables RTF to Internet addresses, the settings in Outlook will not override them.
Global
properties:
<< Outlook 2007 and older: Go to Tools, Options, Email Format, Internet Options button.
Outlook 2010: File, Options, Mail and scroll to the bottom of the dialog. >>
Use this setting to control how messages created using RTF formatting or that require TNEF encoding are handled. If this is set to plain text or HTML formatting, Voting and Meeting Requests may not work unless you override the setting using Email properties.
Recommended setting: Convert to HTML. Outlook will send all messages to the Internet using HTML unless you change the email properties (below).
Email
properties of a Contact - Open the Contact and double click on the email address.
Changes made here apply to all messages sent to this person. Use this to
override the setting in Internet options (above).
Recommended setting for most contacts: Let Outlook decide. This will send all messages using the global properties. If you need to send Meeting Requests or other messages that require TNEF encoding and know the contact uses Outlook, you can set the contact to always use RTF.
Email
properties of an address in the To field of a new message: double click on
the address in the To field. If the address is in your Contacts folder,
their contact opens; if the address is not in your Contacts, the email
properties dialog opens. Use this setting to "one-off" the formatting
when sending meeting requests or RTF formatted messages to Internet
addresses. This will override the setting in Options dialog's Internet
options.
Recommended setting: Let Outlook decide - this will send all messages using the global properties. If you need to send Meeting Requests or other TNEF encoded messages and know the contact uses Outlook, you can set the address to always use RTF.
To access the Email properties of a contact or in the address block in Outlook 2010:
In Outlook 2010 you'll access the email properties from the contact card that
comes up when you hover over or click on an address in a Contact or an email
message. Select the menu icon on the right and then Outlook properties to open the Email
Properties dialog. As with the older versions, the recommended setting is
Let Outlook decide unless you need to force RTF.
Note: If you change the email properties to always use RTF, the autocomplete cache (nickname cache) may remember the setting and will continue to send messages using RTF. Delete the address from the cache to clear it. (Select it using the arrow keys and press Del)
Other causes of unexpected RTF formatting
SharePoint Contact libraries
synced with Outlook are marked to always use RTF.
The Exchange administrator can configure Remote Domain transports for the
domains that don't use Outlook and set them to never use RTF
to get around the problem.
To change the settings on Exchange server, open the Exchange Management Console, expand Organizational Configuration, Hub Transport, Remote Domains, open default transport (or the transport you want to change, if you have more than one) and change the Rich Text setting.
Antivirus scanning corrupts the TNEF attachment and the recipients Outlook can't decode it. This is more common with client side scanners, such as AVG. To fix, disable email scanning on the client side; there is no need to scan email with a virus scanner on the desktop computer.
As mentioned previously, the nickname cache can contain the 'always use RTF' flag - if the sender ever forces RTF for one message to the contact, the cache remembers the setting for that contact and always uses RTF (forcing it on the address overrides the conversion setting in Mail format>Internet), even though the contact is no longer set to always use RTF. Delete the address from the cache to fix.
If nothing seems to be working and you use Outlook 2007 SP2, you can use a registry value to end TNEF encoding once and for all. This will affect your ability to use features that require TNEF encoding - Voting and Meeting Requests in native Outlook format.
More information on this registry fix: When you use Outlook 2007 to send an e-mail message, the recipient of the message sees an attachment that is called Winmail.dat
Hotfix for pre-Outlook 2007 SP2 to enable the registry fix: Description of the Outlook 2007 hotfix package (Outlook.msp): October 28, 2008
If you don't want to make the changes to the registry yourself, you can download a .reg file with the changes. Double click to install.
Outlook 2007 .reg
Outlook 2010 .reg
Before using the registry fix with Outlook 2007, you will need to install the Hotfix for pre-Outlook 2007 SP2
To reverse the changes, delete the key from the
registry or edit the .reg file in
Notepad and change
"DisableTNEF"=dword:00000001
to "DisableTNEF"=-
Utility to decode attachments sent by Outlook that arrive as Winmail.dat files because you sent in Rich Text Format.
Tool for Macintosh computers to decode the Winmail.dat attachment sent in Rich Text Format messages.
Winmail Opener is a small and simple utility that allows users to view and extract contents of TNEF-encoded messages (winmail.dat). Version 1.4 - Free.
Description of Transport Neutral Encapsulation Format (TNEF) in Outlook
Additional technical information on the MSDN Web site
