Allowing my SMTP server to receive emails
Hello. I just built a simple SMTP server. It is incapable of actually sending mail, or even store them. All it does is receive emails and print them to the terminal (I will give it more functionality eventually). By telnetting to it and manually feeding it basic SMTP commands I seemingly managed to write emails to it (it responded according to the protocol and when I did a QUIT it printed a proper looking email). Receiving is all it needs to do, thus so far so good. I do want a bit more than simply using telnet to write mail to it, I want to be able to for example subscribe to a newsletter and receive it on my server (which would currently print it to terminal, though I have other plans to make it bigger).
All things cut short, how can I send mail to my server (or at least, my IP address or its dyndns domain name), WITHOUT needing telnet?