On the General tab, in Default email reader, select Microsoft Outlook. The Mac default is to use the Mail app, but you can change the default to Outlook. Your default mail reader is what's used when you're browsing a web page and share it via email with a friend or colleague, or mail it to yourself for further reading. Under Format and account, clear the Reply and forward using the default e-mail account check box. To change this preference, on the Outlook menu, click Preferences, and then under Email, click Composing. If it is not, click on the ‘General’ button. Step 2: When you open the Preferences box, check to ensure that General screen is activated. Step 1: To set the default email client, you need to first open the Mail app and look for ‘ Preferences ’ in the Mail menu and click on this option. When you forward or reply to a message, Outlook uses the account that the original message was sent to. Steps to Change The Default Email Client on Mac OS. 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.