Reading Winmail.dat files

When you receive an attachment called winmail.dat, it means the sender used Outlook with an Exchange server and encoded the attachment in a format you cannot read on your Mac. It’s like the attached files are in a sealed envelope only Outlook can open.

Here are five ways to solve the problem.

  • Option 1: Ask the sender to attach just one item per email. Sending a message with several attachments at once may result in a winmail.dat file.
  • Option 2: If your email is Google (Gmail)-based, try logging into your email on the web interface. It may be able to decode attachments.
  • Option 3: Download TNEF's Enough on your Mac to manually convert winmail.dat files. See instructions on the web page.
  • Option 4: Install Letter Opener to automatically show winmail.dat as regular attachments in Mac Mail. See below.
  • Option 5: Ask the sender to change their settings so future messages are less likely to create winmail.dat files. Copy and paste the instructions below and give them to the sender.

Please change your settings so I can read attachments you send to me.

  1. Add my email address to your contact list.
  2. Switch to the contacts view and double-click my card.
  3. In E-Mail Properties, check Send Plain Text Only under Internet Format. Save changes.
  4. Recreate the email and attach the files. Then send the email again.
  5. Future attachments will send in standard format without winmail.dat, which makes them readable on my computer.

Using Letter Opener to automatically show winmail.dat as regular attachments in Mac Mail.

  1. Quit Apple Mail if it is running.
  2. Download Letter Opener.
  3. You may purchase the software for $29.95 or use the free trial.
  4. When the installer opens, follow on-screen instructions.
  5. Open Apple Mail.
  6. Open the email and attachments.
  7. Future winmail.dat files will work like normal attachments.

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