XFOR: Preventing Winmail.dat From Being Sent Over IMC


When you send mail over the Internet from a Microsoft Exchange Windows client or an Outlook client, a file attachment called Winmail.dat may be added to the message. This attachment contains the Microsoft Exchange rich-text information of the message being sent. The Winmail.dat file may not be useful to non-Microsoft Exchange recipients. The information in the Winmail.dat file may appear on the receiving end as binary information at the end of the mail message.

This article describes how to prevent sending the Winmail.dat attachment to Internet users when you are using the Microsoft Exchange Internet Mail Connector (IMC).

More Information

You can control whether or not to send rich-text format in any one of the following ways:

  • Custom Recipients
    The administrator can modify an existing Microsoft Exchange custom recipient to prevent rich text information from being sent to that custom recipient by clearing the Allow Rich Text in Messages check box on the Advanced property page of the recipient's properties. You can view the custom recipient's properties by selecting the recipient name and then choosing Properties from the File menu.

  • Addresses in the Personal Address Book
    The user can modify the Internet addresses in their Personal Address Book (PAB) to not be sent rich-text information by clearing the Always Send to This Recipient in Microsoft Exchange Rich-Text Format check box on the SMTP General property page of the Internet address in the PAB. To obtain the properties of an entry in a PAB, select the entry and choose Properties from the File menu.

  • Configuring the Internet Mail Connector (IMC)
    The administrator can configure the IMC to send or not to send rich-text information by following the steps below:

    1. Bring up the properties of the Internet Mail Connector.
    2. Select the Internet Mail property page.
    3. Click on the button labeled Interoperability. This should bring up the Interoperability dialog.
    4. The Send Microsoft Exchange Rich-Text Formatting list box controls the sending of rich-text data. There are three values to choose from:
      • If the value is set to User, the recipient's properties are used to determine whether or not to send rich-text information.

      • If the value is set to Always, rich-text information is always sent, regardless of the recipient's properties.

      • If the value is set to Never, rich-text information is never sent.

    You can also configure whether or not to send rich-text information on a per-domain basis. To define e-mail domains and the message settings for that domain, click the E-Mail Domain button on the Internet Mail page of the IMC Properties. This will bring up the Add E-Mail Domain dialog. Click on the Add button to specify an e-mail domain. Click on the Interoperability button. Select a setting from the Send Microsoft Exchange rich text formatting list box.

  • One-Off Addressing You can send e-mail to an Internet user from a Microsoft Exchange or Outlook client using One-Off addressing. One-Off addressing allows sending a message to addresses that are not in the PAB, the Global Address List (GAL), or in any recipient containers. Depending on the type of the One-Off address used, rich-text information is or is not sent with the message:

    • Rich-Text Information Sent:
      If the One-Off address has the following format, rich-text information is sent with the message:

      [SMTP:<SMTP Address>]

      where SMTP Address is any valid SMTP address, for example:


      To verify that rich-text information is sent:

      1. Select the Check Names command from the Tools menu after typing the address in the above format. This should display the SMTP address without the SMTP:. The name should be underlined.
      2. Bring up the Properties of the address by double clicking it. The option Always Send to This Recipient in Microsoft Exchange Rich-Text Format should be checked indicating that rich-text information (the Winmail.dat file) will be sent along with the message.
      NOTE: Even if you address a message to [SMTP:<SMTP Address>], you can run the Check Names command, then get the properties of the resolved recipient and unselect the Always Send to This Recipient in Microsoft Exchange Rich-Text Format checkbox. This will prevent rich-text information from being sent along with the message.

    • Rich-Text Information Not Sent: If you use a One-Off address and you do not want to send rich-text information to the recipient, the address should have the following format:

      <SMTP Address>

      where SMTP Address is any valid SMTP Address, for example:


      NOTE: Unlike the address in step 4.a. above, the SMTP Address is not proceeded by SMTP: and the address is not enclosed in square brackets. If you click the Check Names command and then get the properties of the address, you can see that the rich-text option is not selected.

    However, no matter what option is selected for the address of the recipient, the IMC settings determine whether or not rich-text information is transmitted. If the IMC is set to never send rich-text data, then even if the properties of the recipient address have the rich-text option selected, no rich-text is transmitted.

    If the IMC has separate settings for individual domains, then the settings for those domains takes precedence for all messages addressed to users in those domains.

Article ID: 149203 - Last Review: Oct 27, 2006 - Revision: 1