See Wikipedia
mailto is a Uniform Resource Identifier (URI) scheme for email addresses. It is used to produce hyperlinks on websites that allow users to send an email to a specific address without first having to copy it and enter it into an email client.
mailto links are a relic of the old internet, they are used to provide an easy way for a user to contact some email on a site. Most often, this creates an unintended user experience where one may unintentionally click on a regular link and it opens up the default mail application.
Often this happens:
My reaction is way too often:
Looks for all mailto links in a page, substitutes the href part to execute some Javascript that just copies the email and shows a little pop up about it.
- Doesn't break the user flow/experience
- Shows what happened upon clicking the url