Winmail.dat received with a Lotus Notes Client

When an Exchange based email organization sends out an email to a non Exchange based organization (Lotus Notes or other systems for example web mailers) it could happen, that a non mapi client receives an empty email with a winmail.dat file attachment.

The client is unable to open the winmail.dat file and so the email is useless for him.

The reason for this is, that the Microsoft internal TNEF alias RTF (Rich Text Format) was sent out of the Exchange organization. There are different places and settings which have an influence, which you may need to check:

1. Domain level (Exchange server settings):


a) Exchange 2003

 In the ESM (Exchange System Manager) go to, Global Settings, Internet Message Format, select the domain. Default domain is “*” but please configure an extra entry for the external SMTP domain for example

If you open the property of the domain and go to advanced, there is a setting "Exchange richt-text format". You can set it to "Always use", "Never use" and to "Determined by individual user settings".

Please set it to never use



b) For Exchange 2007:


Set-remotedomain domainname tnefenabled $false

In the GUI:

Open the Exchange management console, Organization, Hub Transport, Remote Domains, Domain name:

Please set it to never use.



2. Recipient level


Another place where you can configure RTF is at the recipient level.  

a) AD contact

If you got an active directory based contact you can set it to be a non mapi recipient:



Please uncheck the „Use Mapi rich text format) box

Note: For an AD contact there is one additional setting which may need to be set:

InternetEncoding: 1310720

See KB 924240 for more details.

KB 924240        The email message attached with winmail.dat when you send a mail from Exchange to Lotus Notes through a SMTP connector;EN-US;924240 

b) For Exchange 2007:

Open the Exchange management console, Recipient Configuration, Mail Contact:



c) The same is true for a personal contact created in Outlook:



d) Even for a one off addresses this can be set. If you enter the smtp address in the to line for example then do a check names, double click on the email address in the to line,

and you will see the same box as before:



3) Other important Outlook settings:


a) Message Format :

Tools, Options, Mail Format, Message Format (Compose in this message format):

Plain Text, Rich Text, HTML



b) Internet Format:

Tools, Options, Mail Format, Internet Format, Outlook Rich Text options:

When sending Outlook Rich Text messages to Internet recipients, use this format:

-       Convert to Plain Text format

-       Convert to HTML format

-    Convert to Rich Text format



4. Outlook overwriting the Exchange settings:


329454 Outlook 2002 message format overrides Exchange server message format;EN-US;329454

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Options\Mail DWORD:
DisableInetOverride Value: 1

When the registry key is set to a non-zero number, the message format does not override the Internet Message Format that is specified by Exchange.

The key DisableInetOverride still exists in Outlook 2003, 2007 and 2010.


5. NK2 cache


If you have Outlook clients where it sometimes work and sometimes not please delete
the name cache files from the outlook clients (delete username.NK2 file(s))


6. More to read:


821750 How to configure Internet e-mail message formats at the user and the domain levels in Exchange Server 2003;EN-US;821750

290809 How e-mail message formats affect Internet e-mail messages in Outlook;EN-US;290809


Comments (1)

  1. Ben Chudley Booth says:

    I have run into this issue a number of times with/without attachments and sometimes the recommendations re: plain text works. However, a couple times it didn't and I found another fix. Issue was to do with the cached addresses of previously sent emails. So I opened a new email and started typing the recipient's name. As it started to prompt for the address I then clicked the 'x' to delete the cached entry (2007/2010 and Ctrl+Del in <=2003) and manually re-typed the address and hit send. Voila, message received in entirety!

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