Emailed attachments show up as winmail.dat file

If you are attaching a file when creating a new Trello card from email and that attachment is showing up in Trello as a "winmail.dat" file instead of the attached file, you'll need to make some adjustments to Outlook's settings. Outlook can be configured to use a proprietary encoding method that isn't typically understood by non-Outlook mail clients. This is usually referred to as Outlook RTF.

Follow the steps below to change your configuration:

If you're using Outlook 2010, 2013, or 2016:

  • Click on the File menu, and then click on "Options"

  • Click on "Mail" in the left column, and under "Compose messages," make sure "Compose messages in this format:" is set to "HTML"


Changing this setting will ensure that new messages are sent as HTML by default. It's possible to send messages in Outlook RTF if that's been pre-configured, so you'll need to change one more setting.

  • Still in the Mail Options window, scroll to the bottom, and under "Message format," make sure "When sending messages in Rich Text format to Internet recipients:" is set to "Convert to HTML format." This will ensure that any outgoing mail is converted if it's sent to a non-Outlook user like Trello.

If you're using Outlook 2007 or earlier:

  • Click on the Tools menu, and then click on "Options"

  • Under the "Mail Format" tab, click on the button labeled "Internet Format..." in the "Message format" section

  • Change "When sending Outlook Rich Text messages to Internet recipients, use this format:" to "Convert to HTML format"

If you're still seeing winmail.dat attachments:

Outlook has probably saved your Trello email address and is offering to autocomplete it when you start to type the address. You may also have saved the email address to a personal contact. Outlook will save settings in these instances, so you should delete the autocomplete entry or the contact to ensure that Outlook will respect the global settings.


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