To change this preference, on the Outlook menu, click Preferences, and then under Email, click Composing. When you forward or reply to a message, Outlook uses the account that the original message was sent to. When you're finished, under Inbox, click your default account. You can now send email from your non-default email account. To send an email message from an account other than your default account, under Inbox, select the account in the list. In the bottom, left pane of the Accounts box, click Set as Default.
Select the account that you want to make the default account.
Tip: A list of your accounts is in the left pane of the Accounts box, and the default account is at the top of the list.
