General Info/Mail Server CLI
Mail Server Command Line Interface
This page will detail the differences in commands and their respective syntax when communicating with different types of Mail Servers, such as POP, IMAP, & SMTP. Commands should be fairly universal, however keep in mind that each mail server can be configured in any way that its administrator desires, including what commands are accepted and what the responses to those commands are.
Unless you are using an application like openssl, keep in mind that all of your traffic will be in plain text, which is insecure. This could potentially lead to compromise if someone happens to be capturing traffic between your computer and the server.