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Ways To Prevent Outlook 2010 from Sending Winmail.dat Attachment

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What is Winmail.dat Attachment in Outlook 2010?

Detailed information about emails in RTF format gets saved in winmail.dat file. If an email is sent to an email client that is non-supportive to RTF file format (generally a client that is not developed by Microsoft) or an email is improperly converted on Server, the recipients of the message will receive a winmail.dat file as an attachment. 

If an email is composed in RTF format and sent to a client that does not support this format, then a winmail.dat file is sent as attachment for help.”

Winmail.dat File and Other Attachments Missing!

There are times when an email composed in RTF format is sent to a receiver whose client does not support this format. In many cases, the attachments in the mail are sent within the winmail.dat file owing to which the receiver is unable to access the attachment. 

How to Stop Outlook 2010 from Sending Winmail.dat Attachments?

To send an email without winmail.dat file, it has to be ascertained that RTF messages are not sent to people who use an email client non-supportive to RTF format. Some of the very common clients that support RTF format include Windows Live Mail, Outlook Express, Outlook etc. Message Formats according to their compatibility from best to least:
•    Plain Text
•    HTML
•    RTF

In short, we can say that RTF format should be used when there is very high requirement for it and you are sure that the recipient has a client that supports this format. So, what you can do to ensure this? Let’s have a look:

Tip #1: Change Default Message Format 

In Outlook 2010, click on “File”>> Options>> Section Mail>> Compose Messages in this Format 
Tip #2: Use RTF Internally but not Externally 

You can set RTF as default format for emails that are sent internally and RTF/Plain text for the emails that are sent to external contacts.
•    In Outlook 2010, File>> Options>> Mail
•    Click on Group: Message Format
•    Choose the option “When sending messages in Rich Text format to Internet recipients” 

Tip #3: Change Email Format for Every Message

In spite of going for default settings, you can set desired message format every time you create or reply to any message. In Outlook 2010, click on “Format Text” tab and set a format for message. 

This will prevent Outlook 2010 from sending winmail.dat and its adverse consequences. Hope it Helps!
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Expert Comment

I started having WINMAIL issue after installing a fresh new SBS2011.
Before SBS2011, every workstation used to run OUTLOOK 2010 individually and there was no "WINMAIL" issue what-so-ever.
Since I installed SBS2011 and naturally every email is sent out from EXCH2010 in SBS2011, certain recipients started not being able to open PDF attachments because they arrive in the form of WINMAIL.
I posted this question on this board and learned that I had to run the following cmtlet in Exch Shell.
New-RemoteDomain -Name GMAIL -DomainName gmail.com
Set-RemoteDomain GMAIL -TNEFEnabled $false

Once the recipient's domain name is added using commands above, the problem of  WINMAIL.DAT goes away for that particular domain. But then I have to continue to add new recipient's domain name to this date.

I would like to find the permanent solution to this problem. I manage multiple SBS2011 sites and this is only site where users complain that some of their recipients are receiving attachments as WINMAIL.DAT.

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