Tips › Attachments

Open winmail.dat on a Mac

5 October 2026 · searched as open winmail.dat mac

A winmail.dat attachment is Outlook’s wrapper around the real files — sent when Outlook writes a message in Rich Text and the recipient is not on Outlook. Apple Mail shows it as a file nothing can open. MailCode unpacks it.

How to do it

Open the message in MailCode. winmail.dat sits in the attachment strip with an Open button.
Click Open, or the file’s name. The message Outlook packed inside appears in a viewer: its subject, sender, date and text, and every file it carried listed under attachments.
View, Open or Download each file like any other attachment. An Outlook message packed inside it opens as a message of its own.

MailCode: A winmail.dat unpacked: the message Outlook wrapped, and its two files. — A winmail.dat unpacked: the message Outlook wrapped, and its two files.

It works the same for a winmail.dat inside an .eml or .msg file you open from Finder; a winmail.dat saved on its own cannot be opened directly, so open the message it came in. The text of a Rich Text message comes across without its formatting, and its To line reads “undisclosed recipients”, because winmail.dat does not carry them. If you are the one sending them: in Outlook, set messages to HTML under File ▸ Options ▸ Mail.

MailCode is a mail client for Mac and Windows that keeps your mail in a searchable archive on your own disk. Free for 14 days.

Mac App Store Download for Windows