What are POP and IMAP?

When a user sends an email message, the user composes the message using an email client or mail user agent or MUA. An MUA interacts with the user directly, receives the email, and sends it to a mail submission agent or MSA. A mail submission agent or MSA gets an email from an MUA and sends it to an MTA or mail transfer agent. An MTA transfers email messages from one host to another using SMTP. Finally, the email reaches a destination MTA that sends the email to a mail delivery agent or MDA. The MDA receives the email from the MTA and sends it to the recipient’s email client or MUA.

An email message is transferred from one host to another using SMTP. But, if an email client wants to retrieve messages from a mail delivery agent, the email client needs to use a different protocol. POP3 and IMAP are two protocols that are used for that purpose.

POP3 vs. IMAP – What is the difference?

POP or Post Office Protocol is a protocol that works in the application layer, and POP is used by email clients or MUAs to retrieve the email messages of a user from a mail server. The version 1 of the protocol or POP1 was first published in 1984. POP2 was published in 1985. The most commonly used version is version 3 of POP or POP3.

POP3 protocol allows an email client to download all email messages from a mail server, and then it deletes the email messages from the server. POP was widely used when people used to use a dial-up connection. At that time, a user would usually connect to the mail server briefly and then download all the email messages so that the emails can be read later when the user is offline.

So, if a user has multiple email clients, and the user wants to manage his mailbox using various email clients, then POP3 may not be suitable.

Internet Message Access Protocol or IMAP is a protocol that is designed to address the problem. IMAP is also used by email clients to retrieve a user’s emails from a mail server. But, if an email client retrieves email messages using IMAP, the email messages remain on the server even after downloading them. Hence, the user can access the same email messages using a different email client easily.

Also, the IMAP protocol does not delete any email message automatically after downloading it. If a user wants to remove an email message, he has to delete it explicitly from the mail server.

Moreover, when a user reads an email message using IMAP, the mail server stores information related to the state of the message, e.g., whether the email is read or replied, etc. But, POP provides no option to store the state information of a message on the mail server. Thus, it becomes even more difficult for a user to manage his mailbox using multiple email clients using POP3.

POP3 used to be used by older email clients. Nowadays, almost all modern email clients use IMAP to retrieve email messages from a mail server.

I hope this helps. However, readers who want to know more about how various malware and cyberattacks work and how we can prevent them can refer to the book “A Guide To Cyber Security“.

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