Choose the Account Used to Send a Message
You may have various Outlook email accounts for different purposes, for example, a business account, a school account, and an account for a volunteer organization. To specify the account from which you’re sending the message:
In the New Message window, select From. Select the desired account from the list. This is the account name the recipient will see when they receive the email. If you see the Send button, but not the From button, it means your Outlook profile contains only one email account. To view the From button, you’ll need to add another email account.
Change the Default Account
If you use a different account more than the one you set up as the Outlook default account, change the default account to save time and keystrokes.
Go to the File tab and select Info. Select Account Settings > Account Settings. Choose the account you want to use as the default send account, then select Set as Default. Select Close to save your changes and close the window.