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Winmail.dat and Email Attachment Issues

Updated August 9, 2017 at 4:19 PM CST

 

Over the last couple of months we have had an increasing number of people reporting issues with sending email attachments to non-NDSU email accounts.  In most of these cases, instead of receiving the expected attachment, the recipient received a winmail.dat file.

What is winmail.dat?

The winmail.dat file is sometimes used by Microsoft Outlook to store additional information such as text formatting for the message being sent and, under certain conditions, can also contain any files that may have been attached to the email. Unfortunately, winmail.dat stores the attachments in a format that is unreadable on most computers.

Why are some people receiving the winmail.dat file instead of the file I attached?

The problem appears to be linked to contacts we used prior to the email migration last March.  From what we can tell, some contacts that were carried over had additional document formatting added to them by Outlook.  While we're not sure why this happens, we do know that sending mail to the affected contacts will result in an email where the original attachment has been replaced by a winmail.dat file.

What can be done to fix the issue?

In Office 2013 / 2016, the only sure way to fix the issue is to have the sender go into their Outlook contacts and delete and re-create any contacts that are currently receiving the winmail.dat file.

  1. Open Outlook and click on your People tab in the lower left corner.  It can either look like this: Contacts_compact  or this:
  2. Locate the contact for the person receiving the winmail.dat file, right click on it and select delete.
  3. Now click on the New Contact button in the upper left corner of the Outlook window and create a new contact to replace the one you just deleted. 

Once finished, the next email and attachment you send to this person should arrive as expected.

 

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