This is a implementation of simple smtp client, which creating in the scope of programming assignment of the "Computer Networking: A Top - Down Approach" book.

This assignment have next description:

Assignment 3: Mail Client The goal of this programming assignment is to create a simple mail client that sends e-mail to any recipient. Your client will need to establish a TCP connection with a mail server (e.g., a Google mail server), dialogue with the mail server using the SMTP protocol, send an e-mail message to a recipient(e.g., your friend) via the mail server, and finally close the TCP connection with the mail server. For this assignment, the Companion Website provides the skeleton code for your client. Your job is to complete the code and test your client by sending e-mail to different user accounts. You may also try sending through different servers (for example, through a Google mail server and through your university mail server).

So requirements to application is next:

• Application should have possibility to send an emails to any recipient;
• Application should work throught GMail mail services, since without that, probably most mail services will reject incoming messages;
• Application should support gmail authorization;
• Application should implement SMTP protocol;

There is a list of CLI arguments, which supported by an application:

• [-h --host]: information about target host
• [-p, --port]: information about port (TODO by default)