If you find that none of the email links on ArtStation or on your ArtStation website are working, the problem is with your browser and not setting up a default email client. If you don't set up a default email client, no email links will work online - not on ArtStation, not anywhere.
ArtStation uses the universal HTML mailto tag that has existed practically since the internet began.
The tag looks like this:
With webmail becoming more popular, browsers sometimes don't get set up with a default mail application.
The solution for this is to set up an email client with your browser. Google "clicking mailto link nothing happens" to find solutions to your browser.