1. Launch the "Mail" application by clicking on it.
  2. Select "Mail" and "Preferences." Allow the "Preferences" window to pop up.
  3. Choose the "General" button. In most cases, this button's information automatically shows.
  4. Locate the "Default Email Reader" section with the "Mail" application selected. Click on the arrows so that a list of other applications shows. Choose your preferred email client from the list. Choose "Select" if you don't see the program that you want to use; search for it in your "Applications" folder and select it.
  5. Close your mail's preferences window by clicking on the red button on the window's top left.
  6. Return to the "Mail" menu and select "Quit Mail" under it. You have to quit the "Mail" application for your new changes to take effect. The next time you click on an email address or launch your email from an unrelated application, your new default email client will be accessed.