http://binternet.nowherejezfoltodf4jiyl6r56jnzintap5vyjlia7fkirfsnfizflqd.onion/selfhosting/hmail/index.html
If you try to use port 25 (SMTP) to send mails publicly, you will realize that not many ISPs allow it, why ? because most people use it to spam, and to battle against spam, most providers refuse to allow traffic coming from this port. Most commonly you have to ask the support services to allow your ip to use it's port 25 (SMTP).