Article ID: 2487954 - View products that this article applies to.
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 the Winmail.dat attachment.
By default, email messages that are sent from Exchange Online in Office 365 use the Transport Neutral Encapsulation Format (TNEF) format. Messaging systems that aren't based on Microsoft Exchange may be unable to interpret messages that use this rich text format. If the recipient’s messaging system can’t process this format, a file attachment that's called Winmail.dat is added to the message.
Office 365 admins can use Windows PowerShell to change the message format to prevent the Winmail.dat attachment from being sent to external recipients.
To change the message format to prevent Winmail.dat attachments, use one of the following methods.
Scenario 1: Change the message format for external contactsTo change the message format for an external contact that was added to Exchange Online, follow these steps:
Scenario 2: Change the message format for all messages that are sent to a specific domainThis method requires you to create a remote domain object in Exchange Online to control how messages are sent to external domains. You can also use this method to change the message format for messages that are sent to coexistence domains.
For more info about specific Windows PowerShell cmdlets, go to the following Microsoft websites:
Still need help? Go to the Office 365 Community
Article ID: 2487954 - Last Review: October 4, 2014 - Revision: 25.0