SMTP service provider and it is a widely used protocol for sending and receiving electronic mail (email) over a network. An SMTP server, also known as an SMTP relay server or outgoing mail server, is a computer or software application that facilitates the sending of emails from one user or system to another through the Internet. It works in conjunction with other protocols like POP3 (Post Office Protocol 3) or IMAP (Internet Message Access Protocol), which are used for receiving emails.

Here's a basic overview of how an SMTP server works:

Client Initiation: When you compose an email and click "send" in your email client (such as Outlook, Thunderbird, or a web-based service like Gmail), the client communicates with an SMTP server to initiate the sending process.

Establishing Connection: The email client establishes a connection with the SMTP server over a designated port (usually port 25 for unencrypted communication, or port 587 for encrypted communication using STARTTLS). Nowadays, secure connections using TLS (Transport Layer Security) are preferred to ensure the privacy and security of the email content and login credentials.

Authentication: The client provides necessary authentication credentials (username and password) to the SMTP server to verify its identity. This step prevents unauthorized users from using the server to send emails.

Email Transfer: Once authenticated, the client submits the email to the SMTP server. The email is broken down into various components, such as the sender's address, recipient's address, subject, and the email body. The server then processes this information and prepares the email for transmission.

Routing and Delivery: The SMTP server uses DNS (Domain Name System) to determine the recipient server's address based on the recipient's email domain. It then communicates with the recipient server's SMTP server to deliver the email.