How to Prevent Winmail.dat Attachments from Being Sent in Outlook

How to avoid that annoying Winmail.dat attachment

What to Know

  • In Outlook 2010 and up: Go to File > Option > Mail > Compose messages in this format. Choose HTML or Plain Text.
  • In Outlook 2007 and Outlook 2003: Select Tools > Options > Mail Format. Select either HTML or Plain Text.

This article explains how to prevent sending winmail.dat attachments in Outlook. It applies to Outlook 2019, 2016, 2013, 2010, 2007, 2003; and Outlook for Microsoft 365. It includes information on disabling winmail.dat for specific recipients.

How to Prevent Winmail.dat Attachments From Being Sent in Outlook

If Outlook sends a message using the RTF format for bold text and other text enhancements, it includes the formatting commands in a winmail.dat file. Receiving email clients that do not understand this code display it as an attachment. Outlook may also pack other file attachments in the winmail.dat file.

You can get rid of winmail.dat altogether by making sure Outlook does not send mail using RTF.

To prevent Outlook from attaching a winmail.dat file when you send an email:

  1. Go to File.

  2. Select Options.

    Options button in Outlook File menu
  3. Go to Mail.

    Mail category in Outlook options
  4. In the Compose messages section, select the Compose messages in this format drop-down arrow and choose either HTML or Plain Text.

    Compose message format: HTML, Rich Text, Plain Text in Outlook
  5. In the Message format section, select the When sending messages in Rich Text format to Internet recipients dropdown arrow and choose either Convert to HTML format or Convert to Plain Text format.

    Convert to HTML, Plain Text, or Rich Text format menu in Outlook
  6. Select OK.

An illustration showing winmail.dat files attached to an email.

Prevent Winmail.dat Attachments in Outlook 2007 and Outlook 2003

To make sure Outlook 2007 to Outlook 2003 do not attach winmail.dat files:

  1. Select Tools > Options.

  2. Go to Mail Format.

  3. Under Compose in this message format, choose either HTML or Plain Text.

  4. Click OK.

Disable Winmail.dat for Particular Recipients

The standard settings for outgoing mail formats in Outlook can be overridden for an individual email address. If a recipient still receives a winmail.dat attachment after you have made the settings changes, reset the format for individual addresses.

In Outlook 2019 and 2016

  1. Make sure the email address is not in your Outlook Contacts.

    Outlook 2019 and 2016 currently offer no way to change sending preferences for email addresses that are assigned to an address book entry.

  2. Open an email from the desired email address or start a new message to it.

    A new email from Outlook.
  3. Right-click the address.

  4. Select Open Outlook Properties.

    Right clicking on an email address to see the Outlook Properties dialog.
  5. Under Internet format, select Send Plain text only.

    Setting the email properties of the text to plain text only.
  6. Select OK.

In Outlook 2013, 2010, and 2007

  1. Search for the desired contact in your Outlook Contacts.

  2. Double-click the contact's email address or right-click the desired email address and then select either Open Outlook Properties or Outlook Properties.

  3. Under Internet format, select either Let Outlook decide the best sending format or Send Plain Text only.

  4. Click OK.

Extract Files from Winmail.dat Without Outlook

If you receive winmail.dat attachments with embedded files, extract them using a winmail.dat decoder on Windows or OS X.

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