If you're not a user of the Mac Mail app but you use a different email app instead, you can customize your Mac so that your other email app is the default. Once you set it as the default, it'll be opened automatically when you click on an email link instead of the Mac Mail app (which is the default naturally). Here are the steps to change this.

1 - Open the Mac Mail app and select Preferences... from the Mail option in the menu bar.

2 - Click on the General tab if you are not already there.

3 - The first entry will be Default email reader. Set this to be whatever you want to use as your default.