By default, most versions of Outlook will use Microsoft Edge as the default browser for opening links in emails.
However, you can change the default browser within the Options panel in Outlook.
The following step-by-step example shows how to do so.
Step 1: Open Outlook Options
In the top left corner of Outlook, click the File tab.
Then click the Options tab:

Step 2: Open the Advanced Settings
An Outlook Options window will appear.
Click on the Advanced tab:

Step 3: Change Default Browser
Next, navigate to the panel titled File and browser preferences.
Then click the dropdown arrow next to Open hyperlinks from Outlook in and select Default Browser:

Once you click OK, your default browser will be changed to the default browser on your computer.
For example, if you use Google Chrome as your default browser then any links that you click in Outlook emails will be opened in Google Chrome.
Feel free to use these exact steps to change the default browser in your own version of Outlook.
Related Tutorials
The following tutorials explain how to perform other common tasks in Outlook:
Outlook: How to Search Emails by Date Range
Outlook: How to Search for Attachment by File Name
Outlook: How to Export Emails to PDF
Outlook: How to Export Emails to CSV
