Last updated February 7, 2018
Email sent from your connected account shows as being sent on behalf of your Microsoft account.
This is a known issue and will be fixed in a future release. Until then, you can change your From address to be the same as your primary Microsoft account alias.
In the compose window, select > Show From to see the From line.
Select From and choose which email address you want to use.
You can also change your default From address:
In Outlook.com, browse to Connected accounts (Settings > Options > Connected accounts).
Select Change your From address.
Choose an address from the drop-down list and select Save.