In HTML? Nasty, and dangerous: bots crawl for email addresses, which you have to provide as part of your webpage in order to use it. If you don't mind your server being spammed forever, then MAILTO will still work (though it's cumbersome for the user if they use gmail or similar). Google will find you examples.
A better idea is to do it in the codebehind: Simple and safe!
Sending an Email in C# with or without attachments: generic routine.[
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