Simple Message Transfer Protocol (SMTP)
When using SMTP or Simple Message Transfer Protocol, a user is sending, relaying, or forwarding messages from a mail client to a receiving email server.
A sender will use an SMTP server to carry out the process of transmitting an email message to a receiver.
It's important to keep in mind that when thinking about whether to use SMTP or IMAP, that SMTP is about sending mail whereas IMAP is about receiving mail. So, if a user wants to enable email sending within the application, they'll have to go ahead with using SMTP over IMAP.
This means, that in a typical email client setup, a user will use either a POP3/SMTP combination or an IMAP/SMTP combination for their mail needs, depending on their requirements.
How is SMTP Used?
SMTP simply provides a set of codes that simplify the communication of email messages between email servers and users’ computers. Therefore, when a user sends out a message, it's turned into strings of text that are separated by the codes that identify the purpose of each section.
SMTP provides these codes and email server software is designed to understand what they mean. Because SMTP turns a message into a string of text, it is unable to transfer text only. It is therefore not able to handle fonts, graphics, attachments, and other elements of the email message.
For this reason, MIME or Multipurpose Internet Mail Extensions were created to encode all non-text content into plaintext. In that way, SMTP is able to transfer the data as it is intended.
While sending one email is fairly simple, for larger organizations that send thousands of mails for, for instance, marketing or transactional purposes, the SMTP process can get a much more complicated and requires SMTP relay service and custom heaters for multiple recipients.
Why is SMTP Important?
SMTP is important because it provides a common set of guidelines and rules for messages that can be transferred from one user to another user by way of email. Essentially, SMTP is the only way any email can be sent from one email client to another email client through an email server.
As such, it provides a secure environment for sending emails, ensures consistent sending and deliverability, and allows organizations to send bulk emails when they rely extensively on the sending of emails in their business, like for marketing or sales purposes.