What are POP3 and IMAP4?

What is POP3

 While SMTP is a protocol for exchanging mail servers, POP (Post Office Protocol) is a protocol that connects mail servers and end users. Communication is performed using TCP port number 110.

There are several versions of POP, but POP3 is currently the mainstream.

 POP3 stands for "POP version 3". Versions 1 and 2 are now rarely used. Also, compatibility between POP3 and POP/POP2 is not maintained.

POP3 controls which local computers receive e-mail that reaches a specified domain.

 End-users connect to their ISP's mail server via POP3 to retrieve mail stored in their mailboxes.

POP3 can also be described as a protocol that fills the last hop to deliver mail to the local computer.

 However, since POP3 was originally developed only for retrieving emails, it only has a mechanism for unilaterally retrieving emails stored in mailboxes on mail servers, and only on individual local computers. management cannot be performed.

 It is not suitable for use on the go or in a mobile environment, as it retrieves all the accumulated mail when connecting to the mail server.

Therefore, IMAP4 has been developed to store and manage messages on the mail server.

What is IMAP4

IMAP4 is an abbreviation of "Internet Message Access Protocol 4" and is a protocol that can store and manage messages on mail servers.

 With POP3, when connecting to the mail server, all the mail accumulated in the mailbox is retrieved, so mail can only be managed on individual local computers.

 Therefore, POP3 is not convenient for users who use multiple computers, and is not suitable for use on the go or in a mobile environment.

 With IMAP4, you can connect to a mailbox on a mail server online, and select and download only the information you want by looking at the sender and title. You can choose to include only the body of the email or only the attachments.

 As long as you have an environment where you can connect to the mail server online, you can check the contents of the same mail on different computers.

IMAP4 is often used for webmail and mobile mail.

If you explain it like this, IMAP4 seems like a lot of good things, but it's not all good things.

 If you run a mail server with IMAP4, you will have to store and manage the user's mail delivered to your mailbox for a long period of time. Therefore, the server will be required to have a large storage capacity and a certain amount of processing power.

 Also, if the mail server breaks down, all the mail will be lost, so the loss will be greater if the mail server goes down than with POP3. Therefore, considerations such as increasing server redundancy and taking frequent backups are required.