What are SMTP, POP, and IMAP?

If you are using emails on your website or using any email software, you may have heard the terms SMTP, POP3, and IMAP.

These protocols are vital for enterprise companies because they directly affect the emails they send to customers and their ability to deliver them.

Although SMTP is a very technical issue and it is a bit difficult for engineers, it is important to understand SMTP, POP3 and IMAP4 protocols.

What are SMTP, POP, and IMAP?

What is SMTP?

The reason I started with the SMTP protocol is that it is quite different from the way the other two protocols work.

In this case, the Simple Mail Transfer Protocol (SMTP) is commonly used to send e-mail from an e-mail client (Thunderbird, Apple Mail, or Microsoft Outlook) to an e-mail server.

It is also often used to forward or forward e-mail from one e-mail server to another. If the sender and recipient have different e-mail providers, the ability to transfer feeds from one server to another is required.

SMTP uses port 25 as standard, as specified in RFC 5321. You can also use ports 587 and 465. Second, it is now introduced as the preferred port for secure SMTP (SMTPS), which is expected to be outdated. Despite the fact that it is still used by some mail service providers.

What is POP?

The Post Office Protocol or POP is used to retrieve e-mail messages from a mail server to a mail client over a TCP/IP connection. The latest version of this protocol is used all over the world, so it is currently called POP3.

As mentioned in RFC 1939, POP version 3 supports extensions and multiple authentication mechanisms. Authentication features are required to prevent malicious users from authorizing access to user messages.

Generally, POP3 processes messages from customers in this way:

  1. Connects to port 110 of the mail server (995 for SSL / TLS connections).
  2. Receives the e-mail.
  3. Deletes copies of messages stored on the server.
  4. Disconnects from that server.

POP clients may be configured to allow the server to continue to save some copies of downloaded mail. The above-mentioned steps are the most commonly used. Leaving copies on the server is usually an IMAP process.

What is IMAP?

Internet Message Access Protocol (IMAP) is the most advanced protocol in the current version of IMAP4. It allows users to group related messages and save them to folders that can be hierarchically organized later. It also tells you when an e-mail has been read, deleted, or forwarded. Allows users to search mailboxes.

The IMAP protocol generally works as follows:

  1. Connects to the mail server on port 143 (or 993 in the case of an SSL / TLS connection).
  2. Receives the e-mail.
  3. The mail client application remains connected until you download the requested messages.

As mentioned earlier, in this case, the messages are not deleted from the server, they have larger consequences.

How SMTP Works?

Now, if you understand a little better what SMTP means (hopefully), let’s go to what really interests you: the delivery of the e-mail or the “deliverability”.

The SMTP server that you use to send your e-mails is associated with a specific IP address. This IP address is directly used by ISPs to verify the sender’s reputation, so it is directly related to the delivery capacity.

Due to the nature of its services, SMTP servers configured by conventional email providers (Gmail, Yahoo, Outlook, etc.) are not adapted to handle the sending of bulk emails.

This is because IP addresses are not monitored closely, which means that you can send e-mail from the same server as a spam sender. Therefore, if you send bulk emails through conventional email providers, such as those previously mentioned, you may fall into spam.

Difference Between POP3 and IMAP

Basically, the biggest difference between the POP3 email protocol and the IMAP protocol is that the first protocol is not designed to receive and send the other. The main purpose of developing such a mail protocol is to allow the user to manage e-mail without always connecting; this is an excellent advantage for users in most cases. However, there will be a disadvantage when the Internet or telephone connections are weak.

It allows us to download the email when we have a stable Internet connection, and then check it when we are disconnected or out of range.

In contrast, the IMAP protocol allows connected and disconnected operating modes, allowing us to leave email messages on the server until we decide to delete them manually, which then allows us to read them from other computers or mobile devices, such as tablets.

The major disadvantage of the IMAP e-mail protocol is that it downloads and write e-mails that we always have to stay connected to the Internet; this usually requires an additional cost, which may be economically high.

If you do not have an Internet connection when you need to read e-mails, if the messages are not on the computer or device, we cannot perform this operation because they are stored on the e-mail server.



In my personal blog, I will explain the solutions to the problems I encounter in the system, network, and information technologies for you. If you want to contact me or consult about a problem, you can send an e-mail to [email protected]