Here is how to prevent Outlook to sent winmail.dat attachments on iPhone

When sending e-mails from Outlook to iPhone, some of the receivers (who use iPhone) may complain to you that they receive a winmail.dat file they can’t open on their device. Or perhaps you’ve sent e-mails to yourself from an Outlook mail client, and wanted to open that e-mail on your iOS device and you saw the winmail.dat attachment at the bottom.

Example of a winmail.dat file attachment on iPhone

Why do I see winmail.dat as attachment?

The Outlook program is created by Microsoft. Microsoft formats e-mail sometimes as RTF (rich text format), which allows you to use for example bold text. Unfortunately, your iPhone doesn’t know how to handle this and will thus create the winmail.dat file attachment.

Prevent winmail.dat attachments

To prevent winmail.dat attachments, you should use HTML or plain text instead of RTF e-mail messages. Here is a step by step explanation on how to make sure that every e-mail you sent in Outlook is sent as an HTML e-mail.

  • Open Outlook on your computer
  • Go to Options and click on Mail
  • In the Compose Message section, there is the option ‘ Compose messages in this format’: make sure it is put in HTML or plain text
  • In the Message Format section, the option ‘ When sending messages in Rich Text format to Internet recipients‘ should contain the value Convert to HTML format.

Open winmail.dat on iPhone via an app

Preventing winmail.dat attachments is something you can control when you are the one that sends e-mails. However, sometimes you are at the receiving side of things. In this case, you may still want to be able to open that winmail.dat file attachment without necessarily bothering the sender.

There are plenty of free and paid apps on the App Store. Often, the free versions will contain some sort of advertisement. Search for ‘winmail.dat’ on the App Store and you will be able to select from multiple apps. Choose an app that has good ratings and reviews on the app store and try it out.


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