Run the following Windows PowerShell command to confirm that the message format was applied: Set-MailContact -Identity -UsePreferMessageFormat $True Set-MailContact -UseMapiRichTextFormat Never Run the following Windows PowerShell commands to configure the message format as Text Only: For more info about how to do this, go to the following Microsoft website:Ĭonnect to Exchange Online using Remote PowerShell To change the message format for an external contact that was added to Exchange Online, follow these steps:Ĭonnect to Exchange Online by using remote PowerShell. Scenario 1: Change the message format for external contacts To change the message format to prevent Winmail.dat attachments, use one of the following methods. Office 365 admins can use Windows PowerShell to change the message format to prevent the Winmail.dat attachment from being sent to external recipients. If the recipient’s messaging system can’t process this format, a file attachment that's called Winmail.dat is added to the message. Messaging systems that aren't based on Microsoft Exchange may be unable to interpret messages that use this rich text format.
This article describes how Microsoft Office 365 admins can change the message format so that messages that are sent from Office 365 users to external recipients don’t contain Winmail.dat attachments.īy default, email messages that are sent from Exchange Online in Office 365 use the Transport Neutral Encapsulation Format (TNEF) format.