How to Stop Office 365 From Sending Winmail.dat

Winmail.dat is a file that gets created when email clients, usually Apple products like iPhones and MacBooks, can’t interpret the format of an email

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How to stop Winmail.dat from happening

 

The easiest fix is to send your emails as HTML and not Rich Text or Plain Text

You can set your email to HTML in the Format Text tab of any Outlook message

You can set this setting at an organizational level if your Office 365 Admin 

Most, if not all, email clients can process HTML and Plain Text so we might as well default to those and turn of Rich Text because it doesn’t really serve a purpose.

 

How to Turn off Rich Text Formatting in Office 365 admin panel

You will need to be an organizational admin

1. Log into the Office 365 Portal
2. Go to Admin
3. Select the Exchange Admin Center
4. Select – Mail Flow
5. Remote Domains
6. Click Edit on Default
7. Set the ‘Use rich-text format” to NEVER
8. Click SAVE

 

Turn off Rich Text Formatting in Outlook 2010 or new

 

1. Go to File.
2. Select Options.
3. Go to Mail.
4. In the Compose Messages section,
5. Select the Compose messages in this format dropdown arrow and choose HTML
6. In the Message format section, select the When sending messages in Rich Text format to Internet recipients dropdown arrow and choose Convert to HTML format
7. Select OK.

 

Prevent Winmail.dat Attachments in Outlook 2007 and Outlook 2003

 

1. Select Tools > Options.
2. Go to Mail Format.
3. Under Compose in this message format, choose HTML 
4. Click OK.