If you are using Outlook for Windows or Outlook Web App the email will be saved in MSG (.msg) format, if the Outlook client is on a Mac the email will be saved in EML (.eml) format.
For more information on email clients and many other topics, check out our Email channel in the InMotion Hosting Support Center.This article describes how to save an email as an attachment. That completes our guide on making changes to the Outlook email client so that you don’t send a winmail.dat file. In the new Message window, click Insert > Outlook Item. In most cases, the suggestions above will help you sharing large files in Outlook with ease. Services like Gmail offer up to 20 mb of a file to be attached. Email providers do not allow large files to be sent as an attachment. In the Mail view, click Home > New Email to create a new email. Unfortunately, there is no direct way to share a large file that can be attached with an email in a traditional way.
Disable Winmail.dat for Individual Contacts You can make changes to individual contact settings to help prevent sending the winmail.dat file as per the steps below. The instructions should work in recent versions of Outlook but won’t work in Outlook 20 when emails are assigned to an address book entry. These changes are being made so that Outlook doesn’t send or convert messages to Rich Text.
Here you can select HTML or Plain text as per the instructions above. From there, instead of Message Format you will need to find Mail Format. For Outlook 2003 or 2007, you will need to click on Tools to get to the Options menu.