If you've connected another email account to your Outlook.com or Outlook on the web account, you can choose to send email from that address. For example, you might receive a message sent to your Outlook.com account but reply to it using your Gmail address.
To do this, you need to connect another email account to your Outlook.com or Outlook on the web account. See Add your other email accounts to Outlook.com or Connect email accounts in Outlook on the web to learn more.
You can also add an email address in Outlook.com and send email from that address.
Send email from a different email address
In the compose window, select > Show From to see the From line.
Select From and choose which email address you want to use.
Change your default From address
Note: Currently, it's not possible to change your default From address in the Outlook.com beta. To change your default From address, turn the beta off, follow the instructions below, and then turn the beta on again.
At the top of the page, select > Options or Mail.
In the Options pane, under Mail > Accounts, select Connected accounts.
Under From address, select Change your From address.
Choose an address from the drop-down list and select Save.