Open the Preferences menu, then select General.If you are able to open the Apple Mail app (most people do since it comes preinstalled with macOS), the steps to configure Outlook as your default email app are as follows: Making Outlook the default email composition app Additionally, you may want to make Outlook the default app to open email files, which normally end in an. If you want to use Outlook as the email app on your macOS computer, so that when you click on an email address like it opens Outlook automatically, you need to configure it first.