How Mail Protocols Work

You have probably heard about the POP3 or IMAP settings. When setting up your email account on your mobile you must specify what account you want to add. Often you will be asked if you want to add a POP3 or an IMAP account.

POP3 and IMAP are email protocols. A protocol is the way the device communicates with a mail server. There are a number of email protocols, each mail protocol has its own advantages and disadvantages. Protocols used for the mail are: POP3, IMAP, SMTP and MAPI. But mail can also be received via another protocol via the HTTP or HTTPS protocol.

mail protocols

Here we have covered some major mail protocols and explained how each protocol works.

POP3 protocol

The POP3 protocol is the most recent version of POP. POP (Post Office Protocol) is an internet standard for transferring an email from a server to a client. With the POP3 protocol, e-mail messages are retrieved to the client mail program, messages are in most cases removed from the server.


  • Not suitable for mail on multiple devices
  • No synchronization, it is only retrieval and removal
  • Email data stored on your own computer


  • Consumes little bandwidth
  • Mails picked up quickly
  • POP3 server can be linked to almost any email program

IMAP protocol

The (IMAP) Internet Message Access Protocol is an email synchronization protocol. The emails at IMAP are both on the computer (caching) and on the server.


  • Only suitable for synchronization of Mail
  • Continuous connection to server for synchronization
  • Synchronization of Calendar and Contacts not possible


  • Synchronization with multiple devices possible
  • In the event of a system crash, you can quickly retrieve the data
  • Emails stored on the server

SMTP protocol

The SMTP protocol send messages from client to server. But servers also use this protocol to communicate with each other. Suppose you have set up an IMAP account in Outlook with an outgoing SMTP server, the following process takes place when sending an email. The entire process runs on the SMTP protocol.

  • Client sends an email
  • Client computer sends the mail to its own mail server
  • Own mail server views the recipient of client sent message
  • Own mail server contacts the recipient’s mail server and delivers the message

Outbound SMTP

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HTTP / HTTPS protocol

The HTTP protocol is mostly used for web page transfers. The brother of HTTP is HTTPS where the letter S stands for Secure. When connecting to HTTPS, the connection to the server becomes encrypted, the killer of an encryption. For mobile devices, Microsoft has developed a service called ActiveSync. With ActiveSync, data is synchronized over HTTPS connection to the server. ActiveSync is mainly used for mobile devices.

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