That question is a bit out of our scope, but we can answer it anyway:
The prefix "mailto:" is a registered URI prefix that is recognized by most, if not all browsers. What it does is upon clicking the link, it will open the default e-mail program, provided that there is one.
In addition, depending on the exact syntax of the link, the email program may populate some fields like TO, FROM, SUBJECT, BODY and others.
Once the user clicks "send message" in the email program, the message will be processed in accordance to the users settings. If the user does not have settings, he / she will go trough a basic wizard with few steps to enter credentials, servers and other information needed to send a message.
I hope that helps.
the Telerik team
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