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The winmail.dat attachment

Posted by at HostingXtreme on Comments Off on The winmail.dat attachment

We are often asked by our clients:

I am receiving email from some email addresses, with an attachment called winmail.dat. I am able to download the attachment but not able to see the contents or open it. How do I see the winmail.dat attachment? My Anti-virus shows that it is clean and virus free.

To address, this issue, we have come up with these frequently asked questions on winmail.dat:

What is winmail.dat?

To put it simply, it is an issue, with the senders Microsoft Outlook or Outlook Express email client. It is not related to our server or our webmail service. Nor is it a problem with your computer or operating system.

This file contains formatting information put by Microsoft Outlook, to decode any attachments sent with the original message.

Why is the winmail.dat file sent?

When people send messages from incorrectly configured Microsoft Outlook email clients, a file called winmail.dat is attached to the message automatically.

Why can’t I open the winmail.dat file?

The winmail.dat file is not recognized by other email clients like Thunderbird, Apple Mail and other webmail clients like Horde, Roundcube etc.

If you download or open winmail.dat, you will be prompted to specify the application that should be used to open the file.

How can the sender prevent this winmail.dat bug?

To prevent this file from being attached to messages, the sender can configure various options given by Microsoft

  • https://office.microsoft.com/en-us/outlook-help/recipients-receive-a-winmail-dat-attachment-HA010153018.aspx
  • https://support.microsoft.com/kb/278061

To reiterate, this is not an issue related to the webmail or mail server. This bug can only be resolved by the sender.

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