A Server is a type of Software that provides services to users or terminals that request it. For example, in a typical client-server architecture, the client could be a computer that makes requests for information through a mail program (Outlook Express for example) and, the server delivers the data in the form of e-mails in response to your request.
E-mail is a service that allows the exchange of messages via electronic communication systems.
The concept is mainly used to name the system that provides this service via the Internet using the SMTP (Simple Mail Transfer Protocol) protocol, but it also allows naming other similar systems that use different technologies. E-mail messages make it possible to send, in addition to text, any digital document (images, videos, audios, etc.).
A mail server is a server that allows me to exchange e-mail messages, either between users, client, and server. The mail server hosting stores and forwards mail messages, this is probably the most used TCP/IP application.
This allows us to keep in touch with people from different places without having to do it using letters, telephone, etc.
SMTP, Simple Mail Transfer Protocol: Known as Transport Protocol, is the protocol used for sending mail either from one mail server to another or from a client of e-mail via a hosted SMTP server.
The delivery of mail from a Client application to a server and from a source server to the destination server is handled by the Simple Mail Transfer Protocol (SMTP) The main objective of the Protocol Simple Mail Transfer Protocol, SMTP is to transfer e-mail between mail servers. However, it is critical for mail clients.
To send mail, the client sends the message to an outgoing mail server, which contacts the destination mail server for delivery. For this reason, it is necessary to specify an SMTP server when you are configuring a mail client as long as we do not use Web-based e-mail (Webmail).
An important point about the SMTP protocol is that it does not require authentication. This allows anyone on the Internet to send mail to any other staff or large groups of people. This SMTP feature is what makes junk or spam possible.
Modern SMTP servers host try to minimize this behavior by allowing only known hosts (PCs) to access the SMTP server. Servers that do not place such restrictions are called open relay servers — mail access protocols.