I work with people who prefer Outlook as their primary email client. Occasionally, they will store copies of important emails to our company’s file server in the Outlook file format with a *.msg file extension. To open these Outlook files in Thunderbird, I use a pure Ruby program called mapitool, which is able to convert my_import_email_message.msg to my_import_email_message.eml.

To use the tool, you will need to install the ruby-msg gem, which will install a new program called mapitool.

$ gem install ruby-msg

To convert the fictions email message above, I would execute the following command.

$ mapitool -i my_import_email_message.msg

Mapitool will create a new file with the *.eml extension, which I can now open directly in Mozilla’s Thunderbird email client.

Happy hacking.

– Chris


  1. Thunderbird
  2. Outlook
  3. Outlook Msg File Format
  4. Mapitool
  5. Ruby-Msg Gem