Email recipients receive a Winmail.dat attachment from Entourage for Mac users in Office 365

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Problem

Email recipients receive Winmail.dat file attachments from Microsoft Entourage for Mac users in Microsoft Office 365. The following are two scenarios in which users experience these symptoms:

An Office 365 user creates and sends an email message by using Entourage. When the recipient receives the email message, the message contains a Winmail.dat file attachment.�
An Office 365 user receives an email message from a sender who uses Entourage. When the Office 365 user receives the email message, the message contains a Winmail.dat file attachment.

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Cause

This issue occurs if an Entourage user sends a message by using an encoding format that isn't supported by Microsoft Exchange Online.

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Solution

To fix this issue, the sender must�set the encoding format for messages in Entourage.�

To set the encoding format in the settings for Entourage, follow these steps:

In Entourage, click Preferences.
Locate Mail & News Preferences, and then click Compose.
Under Attachments, set the Encode for option to Windows (MIME/Base64).
Click to select the Append file name extensions check box.
Exit Entourage, and then restart it.

To set the encoding format for a single message, follow these steps:

In Entourage, on the File menu, click New, and then click Mail Message.
Type the email address of the recipient in the message, and then close the address window.
Under Attachments, click Encode for any computer.

Note By default, the AppleDouble option is selected.
Under Encode for, click Choose Windows (MIME/Base64).
Click OK, and then send the message.