To clarify, all browsers CAN handle the mailto link as long as the user configures it to open the correct email client. That’s key because there’s many oblivious users who don’t even know about this setting (we know from the number of support requests we get from users angry that the contact link they created on their websites “don’t work”!). :)

Because of the prevalence of webmail like gmail (most of our users are on gmail) there’s many users who aren’t aware that it needs to be configured to open the said webmail page, so the mailto links does nothing. A “Contact me” or “contact support” mailto link won’t open anything, or it will open the default mail client like Mac Mail on Mac....On Windows in the past it would open outlook express lol. :)