If you use several e-mail accounts, you can define which one you want to set as default so that it is always processed first. Outlook will send your messages via the default account unless you select another account via the Accounts button.
This is what you do:
1. Click the File tab.
2. Click Account Settings and then select Account Settings.
3. Click the name of the account.
4. Click Set as Default.
5. Click Close.