Outlook Email Attachment: Winmail.dat

Have you ever received an email with an attachment called Winmail.dat?  Alternatively have you ever sent someone an attachment only to have them tell you it came through as a Winmail.dat file?  If this has happened to you in the past, Microsoft owes you an apology. This didn't happen because of a corrupted file, or a flaky server. It happened because of a bug in the way Outlook interfaces with internet based email. The good news is that we can fix it, and prevent it from happening again.

The behavior occurs when someone is sending an email attachment using Outlook to a webmail account, and the email uses rtf format. The recipient will be unable to open the Winmail.dat attachment, (which appears to be corrupted).  

Interestingly, if the recipient forwarded the message on to someone else, or even sent it back to the sender, it would show up in its native format with the attachment. The problem does not occur if Outlook is used on the transmitting AND receiving end. 

If you use Outlook and want to prevent sending out Winmail.dat attachments, just follow these simple steps:

Go to Tools > Options




Click the Mail Format tab





Click Internet Format




Select either "Convert to Plain Text format" or "Convert to HTML format" under "Outlook Rich Text Options".

Easy!

There are also several winmail.dat decoders out there... here's an example.

Sometimes you'll find you go through the process above and there are still some people who receive your attachments as winmail.dat files. If this happens, you'll have to change that person's contact settings individually.

To change the default settings for an individual contact, go to:

Tools > Address Book > Click on Contact > Double click their email address > Change the pull down option under Internet Format to "Send in plain text only"

To change the settings for an individual email, open a new message window > Options > Click plain text.

Still having issues?  Let me help.