If you set up multiple email accounts in Microsoft Outlook, you can choose which account to use when you send a message.
In the message window, above to To button, click From.
Click the account that you want to use.
By default, email is sent by using the account that you designate as the default in the Microsoft Office Backstage view. For example, your default account might be your work email account, but you can choose to send a message from another email account, such as your personal Internet service provider (ISP) account.
Sending messages from your ISP account may require you are connected to that provider to receive permission to use the email server. Contact your network administrator or ISP for more information.
Why is the From button is missing?
If you see the Send button, but don’t see the From button, your Outlook profile contains only one email account. To add another email account, see Add or remove an email account.