What is SMTP?

SMTP (Simple Mail Transfer Protocol) is a set of communication guidelines that allow software to transmit an e-mail over the internet is called SMTP. This program is used for sending message to other computer users based on electronic mail addresses. It is the Application Level protocol that handles message services over TCP/IP networks.  

SMTP provides a mail exchange between users on the computers (same or different), and this also supports: 

Sending message can include a single message to one or more recipients. 

It can send text, video, voice or graphics. 

Also, it can send the messages on networks outside the internet. 

Its main purpose is used to set up communication rules between servers. Interconnected network of email servers that follows the same set of rules. Emails can find their way across the Internet & reliably reach their recipient’s inboxes the moment they’re sent.

Note – SMTP is a core element of online infrastructure, embedded in modern communications just like SMS & cell towers. Same standards universal applications ensures that the Internet can function as intended. 

How Simple Mail Transfer Protocol (SMTP) Works ?

SMTP is the system we use to send emails effectively and it is based on end-to-end message delivery.  Email servers have special SMTP servers, generally formatted as smtp.mailserver.com, that handle sending email for many addresses at once. You can generally find your SMTP email server address in the account or setting portion of your mail client. 

An email address format is part of the underlying rule set of SMTP. The recipient’s SMTP server is found based on the domain name of the email & appears after the @symbol. The mailbox on this server is found by the name before the @symbol. 

Also its responsibility is matching email to the sender’s address but it’s a trust based protocol. If the sender spoofs their email address, SMTP has no way to detect or stop this.   

What's the Mapping Journey of an Email With SMTP ?

It is responsible for moving email to the recipient’s inbox from outbox, using a system called store & forward. Messages are sent to the nodes (intermediate servers), then routed & organized as required. This creates a chain of places where a message can be temporarily stored as it jumps from node to node. 

Because of these intermediate nodes, The SMTP network is delay tolerant, which means that it can handle intermittent connections to the service. A direct connection between sender & recipient is also not required. Mostly postal services use a similar system, sending mail to intermediate centers to sort & distribute it as efficiently as possible. 

A user sends an email by composing an e-mail message using a Mail User Agent (MUA). It (MUA) is a program which is used to send & receive mail. If the domain name of the recipient’s email address is different from the sender’s domain name, then MSA will send the mail to the Mail Transfer Agent (MTA). Which uses the DNS system to look up the mail exchanger (MX) server address that maps to the domain name of the recipient’s email address. Then MX server uses internal records to route the message to a mail delivery agent (MDA), which eventually forwards the message to the recipient's inbox.

If the emails are sent within the same domain, e.g. The message may not need the MX server between the same company employees. Most of the emails (Not all emails) are sent with that chain of communication. 

 Why is the SMTP Protocol Important?

Without SMTP server, an email wouldn’t make it to its destination. When you click ‘send’, your email transforms into a string of code that is then sent to the SMTP server. The SMTP server verifies that the outgoing email is from an active account, acting as the first safeguard in protecting your inbox from illegitimate email. If it can’t be delivered, it will send the email back to the SMTP sender. This informs the sender that they have the wrong email address or that their email is being blocked by the receiving server.