SMTP is the system that sends your emails from one computer to another across the internet.
What is SMTP?
According to a study on SMTP, “Most e-mail systems that send mail over the Internet use simple mail transfer protocol (SMTP) to send messages from one server to another. The messages can then be retrieved with an e-mail client using either post office protocol (POP) or Internet message access protocol (IMAP).”
SMTP is the main system for sending emails across the Internet. Imagine it as a digital post office that handles millions of messages, routing them from senders to recipients efficiently and reliably. SMTP coordinates with other protocols to verify that emails go to the right addresses without errors. It’s a necessary component of everyday communications, making it possible for messages to travel across the world in seconds.
When is SMTP used?
SMTP is the standard email protocol and is widely used for corporate and personal email systems. It works behind the scenes whenever you send an email via popular email clients or web-based services like Gmail or Yahoo Mail.
See also: Develop and enforce robust email policies and procedures
How Does SMTP Work?
Initiation of communication
The process begins when a user sends an email. The email client (a Mail User Agent or MUA) uses SMTP to communicate with its configured outgoing mail server (an SMTP server or Mail Transfer Agent - MTA). The SMTP session is initiated with a 'handshake' between the client and the server. This usually involves the client sending a command like HELO or EHLO to introduce itself to the SMTP server.
Sending email information
Once the handshake is successful, the email client sends the email's metadata using SMTP commands. This includes the sender's email address (MAIL FROM command), the recipient's email address (RCPT TO command), and other necessary headers.
Transmission of the email content
The email client issues the DATA command, signaling that it is about to send the message body. The actual message data, including the subject and body of the email, is transmitted. In cases where the email includes attachments or non-ASCII text, these are encoded appropriately (often using MIME - Multipurpose Internet Mail Extensions) so they can be transmitted over SMTP.
Routing and delivery
The email is directly transferred to the recipient’s mail server if the sender and recipient are on the same domain. If they are on different domains, the SMTP server queries a Domain Name System (DNS) server to find the Mail Exchange (MX) record of the recipient's domain, which tells it where to forward the email. The sender's SMTP server then connects to the recipient's SMTP server (or an intermediate relay if necessary) and transfers the email.
Queue and retry mechanism
Suppose the recipient’s SMTP server is unavailable or busy. In that case, the sender’s SMTP server places the email in a queue and periodically retries sending it.
Final delivery and receipt by client
Once the recipient’s SMTP server accepts the email, it stores the message, usually in a queue. The recipient retrieves the email using an email client configured with a mail retrieval protocol such as IMAP or POP3.
Session termination
After the transfer, the SMTP client sends a QUIT command to close the connection.
See also: HIPAA Compliant Email: The Definitive Guide
How Does SMTP Differ from IMAP and POP3?
While SMTP is specifically designed for sending and relaying emails from the sender's server to the recipient's server, IMAP and POP are used for receiving and retrieving emails from a server to the user's email client. IMAP allows users to access and manage their emails directly on the server, enabling synchronization across multiple devices. On the other hand, POP typically downloads emails from the server to the user's device, often deleting the original from the server. In essence, SMTP handles the outbound dispatch of emails. In contrast, IMAP and POP govern those emails' inbound retrieval and local management.
See also: Empowering patients through HIPAA compliant email solutions
FAQs
What is an email protocol?
An email protocol is a set of rules that helps send and receive emails over the internet.
What is TLS?
Transport Layer Security is a security protocol that protects data as it travels across the internet, keeping your information safe from hackers.
What is AES?
Advanced Encryption Standard is a method used to secure and scramble data to prevent unauthorized access.
Kirsten Peremore
