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).
The problem? Any attachments included in the message are encased in the winmail.dat attachment.
Note that if you are using (or administrating) Exchange Server, the Exchange administrators can disable RTF on messages sent to the Internet. SharePoint Contacts linked to Outlook are also a problem. See Other causes of unexpected formatting for more information.
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. If there is an attachment in the winmail.dat, asking for a resend is my preference, in most cases. This way the sender fixes the problem for future attachments. If you aren’t expecting an attachment and the file size is too small for an attachment, you don’t need to ask for a resend, you are only missing the pretty formatting.
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):
- The formatted text version of the message (ie, font and colors).
- OLE objects (such as embedded pictures and embedded Office documents).
- Special Outlook features (i.e., custom forms, voting buttons, and meeting requests).
- Regular file attachments that were attached to the original 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.
Don’t forget to clear the auto-complete cache after changing Outlook’s settings. The autocomplete cache (nickname cache) remembers the setting and Outlook will continue to send messages using RTF. Delete the address from the cache to clear it or clear the entire autocomplete cache. See How to clear name from the cache at Understanding Outlook’s Auto-Complete Cache if you need help clearing the autocomplete cache.
Global properties:
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.
Outlook 2007 and older (below, left): Go to Tools, Options, Email Format, Internet Options button.
Outlook 2010 (below, right): File, Options, Mail and scroll to the bottom of the dialog.
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 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.
Reminder: The autocomplete cache (nickname cache) may remember the RTF setting and Outlook will continue to send messages using RTF, overriding the Contact settings. Delete the address from the cache to clear it. (Select the address 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. This is fixed in Outlook 2010 SP1 or 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 all else fails…
If nothing seems to be working and you use Outlook 2007 SP2 or Outlook 2010, 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, including Voting and Meeting Requests in native Outlook format. (Ready-to-use .reg files are available below.)
- Close Outlook
- Start Registry Editor (type regedit in the Start Search box or Start menu, Run command and press Enter)
- Locate the following registry key:
In Outlook 2007:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PreferencesIn Outlook 2010:
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences - Add a new DWORD named DisableTNEF.
- Double click on DisableTNEF and in the Value data box, type 1
- Close the Registry editor and Restart Outlook
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
Do It For Me
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
Remember to restart Outlook or reboot if the registry key does not appear to work!
To reverse the changes, delete the key from the registry or edit the .reg file in Notepad and change the following line, then save and run it.
“DisableTNEF”=dword:00000001 to “DisableTNEF”=-
Tools to Recover Attachments from Winmail.dat
Tools
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. |
More Information
Description of Transport Neutral Encapsulation Format (TNEF) in Outlook
Additional technical information on the MSDN Web site
E-mail attachments are not visible to some recipients
How e-mail message formats affect Internet e-mail messages in Outlook
XADM: Winmail.dat Attached to All Internet Messages Regardless of Setting on Client
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Last reviewed on Dec 1, 2011
This is an excellent article. However I still have a few queries.
It is still a mystery why only some of the email addresses in my contacts file came to be set to “always use RTF”. There seems to be no pattern. Any suggestions?
Is there a quick way of checking the email format setting for 1000 plus contacts and changing it to “Let Outlook decide” where necessary? i.e. is there a default setting for the email address format which will apply to all contacts.?
How do I make sure that no new addresses creep into the file with the “always use RTF” setting attached?
I have inserted the registry value to end TNEF encoding, which will presumably do this, as I am unlikely to need the voting and meeting requests facilities in native Outlook. Is this the only solution.
See http://www.slipstick.com/outlook/contacts/let-outlook-decide-the-best-message-format-to-use/ – there is a link to a VBA sample that changes the setting on many contacts at once.
AS for how that came to be set – it’s impossible to know. It’s possible an older version did it, an import, sync… almost anything. Sharepoint contacts always use RTF – that is fixed in Outlook 2007 /2010 if you have all updates installed.
No default oprion – it should default to let outlook decide. The only way they’d creep in is if you imported or synced – but normally, sync doesn’t cause it.
I did it all, and yet- when sending emails from our outlook users – allways send as winmail.dat.
I use exchange 2010 / outlook 2007+2010
Please help?
dont work… still same crap
What version of Outlook and what type of email account do you have configured it in? Did you restart Outlook or reboot the computer after setting the registry value?