Your question looks like - can I show webpages to users without a web-server? Yes you can if you are able to write your own web-server.
Can you write SMTP server on Go? Yes. Google shows few solutions for "golang smtp server" query. So I'm pretty sure you can integrate SMTP server functional into your application.
But as commenters said - most part of your messages (if not all) would go directly to spam folder on most part of services.
