Stop Apple Mail App From Opening Email Links in Browser in One Quick Step
On macOS, clicking an email or “mailto” link in whatever browser you use automatically opens Apple Mail, the default mail application. Stack Exchange user Randy Marsh suggests making quick adjustments to prevent Mail from accidentally starting.
To fix the auto-opening issue, open the Mail app, select Mail from the menu bar, and go to Settings. You can also use the “⌘ +” shortcut. From there, you can change the default email app to whatever app you need.
Marsh instructs you to select Finder located in the CoreServices folder (HD -> System -> Library -> CoreServices -> Finder.app). When you click on the link, you simply switch to a Finder window instead of opening a new application.
If you use the Internet a lot, just select your preferred browser in the Applications folder. From now on, clicking an email will simply leave you in the same browser window, essentially disabling the auto-open feature.
Automatically opening Apple Mail can be handy for those who actually use it, but for people who use webmail services like Gmail or Outlook, opening an unneeded app after clicking on each email is annoying, especially when one and the other the same can be done by copying and pasting the email link.