[CONTENT] Implement an FTP and SMTP example

Implement an example of FTP and SMTP servers. Depending on the complexity to explain, you can just create an article and demonstrate the concepts in an already consolidated API. If the level is "medium", then prefer to show the implementation.

The preference to show the implementation is because to understand how it really works we must see the code line, which makes it clear that this protocol is not "magic", but rather an application of a lower level concept.