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Microsoft Exchange - How to Prevent the Winmail.dat File from Being Sent to Internet Users

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This article describes how either an Exchange Server administrator or end users can prevent the Winmail.dat attachment from being sent to Internet users when using the Microsoft Exchange Internet Mail Connector (IMC).

When an end user sends mail to the Internet from an Exchange Windows or Outlook client, a file attachment called 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). The Winmail.dat file contains Exchange Server RTF information for the message, and may appear to the recipient as a binary file. It is not useful to non-Exchange Server recipients.


To control whether or not to send messages in RTF, follow the option that best meets your situation:
Creating Custom Recipients
When an administrator creates a custom recipient using the Microsoft Exchange Administrator program, click to clear the Always Send To This Recipient In Microsoft Exchange Rich-Text Format check box.
Modifying Existing Microsoft Exchange and Custom Recipients
An administrator can prevent an existing user account (Microsoft Exchange user or custom recipient) from sending RTF information by clicking to clear the MAPI Recipient check box on the Advanced property page of the recipient's properties. An administrator can view the recipient's properties by clicking the recipient name, and then clicking Properties on the File menu.
Addresses in the Personal Address Book
End users can modify the Internet addresses in a personal address book (PAB) to prevent sending RTF information by clicking to clear the Always Send To This Recipient In Microsoft Exchange Rich-Text Format check box in the SMTP - Address property page of the Internet address in the PAB. To obtain the properties of an entry in the PAB, click the entry, and then on the File menu, click Properties.
Configuring the Internet Mail Connector (IMC)
An administrator can configure the IMC with RTF options in the following manner:
1.Open the Internet Mail Connector Properties page.
2.Click the General tab.

The Send Microsoft Exchange Rich Text 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 properties are used to determine whether or not to send RTF information.
If the value is set to Always, RTF information is always sent, regardless of the recipient properties.
If the value is set to Never, RTF information is never sent.
An administrator can also configure the option to send RTF information on a domain-by-domain basis. To define e-mail domains and the message settings for that domain, click the E-Mail Domain button of the Internet Mail tab.
One-Off Addressing
Anyone can send e-mail to an Internet user from an Exchange or Outlook client by using one-off addressing. One-off addressing allows you to send a message to addresses that are not in the PAB, the global address list, or in any recipient containers.

Depending on the type of the one-off address used, RTF information is or is not sent with the message:
Rich-Text Information Is Sent:

If the one-off address has the following format, RTF information is sent with the message:

[SMTP:SMTP Address]

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

[email protected]

To verify that RTF information is sent:
1.In a new message, type the address in the SMTP address format in the To field. On the Tools menu, click Check Names. You will see the SMTP address without the "SMTP:" and the name is underlined.
2.Double-click the address to bring up its properties.

If the Always send to this recipient in Microsoft Exchange rich-text format check box is selected, rich-text information (the Winmail.dat file) is sent along with the message.
Rich-Text Information Is Not Sent:

If an end user is using a one-off address and does not want to send RTF information to the recipient, the address should have the following format:

SMTP Address

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

[email protected]

NOTE: Unlike the address in the "Rich-Text Information Is Sent" section, the SMTP address is not proceeded by "SMTP:" and the address is not enclosed in square brackets ([]).

If the Check Names check box is selected, the properties of the address will show 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 RTF information is transmitted. If the IMC is set to never send RTF information, even if the properties of the recipient address have the rich-text option selected, no RTF information is transmitted.

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

Optionally, instead of typing the hex value in the edit field, click Editor, select File Version, and then click OK. On the File Version tab, in the fields provided, type the appropriate build number of Imcadmin.dll in the following format 5.5.2650.24. To determine the correct build number of Imcadmin.dll, do a search for the file on the Exchange Server. Once you have found it, right-click it, click Properties, and then click the Version tab. The build number appropriate to your server is listed here. Type this number into the value field and click OK. You then see the appropriate Hex value in the edit field.

Microsoft Exchange Client 5.5
Microsoft Exchange Client 4.0