Outlook uses .msg Files.
Select an email on the message list, click the File menu and choose the Save as option. The Save As dialog box will open. Point to the desired folder and choose Outlook message format or Outlook message format - Unicode from the file type drop-down menu
Click on New > Email message.
On the message list, select an email you want to export and drop it onto the body of the new email.
Click on ”More”.
Click on ”Download (.eml)''.
File is as .eml downloaded.
Select the email.
Then the file is saved as mymessage.eml, which you can send as an email attachment.