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SMTP and IMAP: What’s The Difference Between These Protocols?

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People send billions of emails daily, but most people don't know about the internal processes that enable this massive exchange of information. It works because email protocols define how a message is transferred between various mail servers.

SMTP & IMAP are the most popular protocols you'll come across, and this article will explain their differences.

What Is SMTP?

It stands for Simple Mail Transfer Protocol (SMTP). It defines rules mail for exchanging outgoing mail between senders and receivers.

How Does SMTP Work?

The most important aspect of it is the mail server. EServers power every email exchange. You transfer a message from your mail server to another whenever you click the send button. Your email client (Gmail, Yahoo Mail, etc.) sends your messages to an SMTP server, which decides the correct server to relay the message to. Here's a step-by-step breakdown:

  • A mail user agent (MUA) connects your domain's SMTP servers; this connection is called a handshake and is carried out via a port (25, 465, 587, or 2525).
  • The client gives the sender's and recipient's mail addresses alongside the message body and attachments to the server. 
  • The mail transfer agent (MTA) checks if the sender's and recipient's domain names are the same. If so, it transfers the message directly to the recipient's servers. If the domains differ, the server communicates with the Domain Name System (DNS) to identify the recipient's IP address. With the IP address, it identifies the correct servers to pass the message to.
  • The recipient's server verifies the incoming message and forwards it to the email client; the recipient can then open it.

What Is IMAP?

It stands for Internet Message Access Protocol. It's similar to the other but with a core difference; SMTP sends data while IMAP retrieves data. IMAP enables users to organize messages on their server, while the other lets users organize notes on the email client.

How Does IMAP Work?

This protocol is an intermediary between the mail server and the client; you can read messages stored on the servers without downloading them. Hence, you can access emails from any device and location with the correct login details.

Here's a step-by-step guide:

  • You log in to your mail provider and connect with the IMAP servers. Most email clients support this protocol.
  • IMAP uses a port to connect your email client and the servers. 
  • Once logged in, the provider shows you a preview of all recent incoming messages. When you want to read a message, click on it, and IMAP will immediately display it. The message remains stored on the server. It won't be deleted unless you do that yourself.

Differences Between IMAP and SMTP

As mentioned, SMTP is for sending messages, while IMAP is for retrieving messages. Both protocols are necessary for you to get and read your emails.

  • The former transfers messages from a client to a server, while the latter transfers messages from a server to a client.
  • SMTP uses ports 25, 465, 587, and 2525, while the other works on ports 143 and 993.

Can You Use Your Servers?

Yes, you can run your own SMTP or IMAP servers. However, using an external one is advisable; you can choose the best SMTP service. The main reason not to use your mail servers is that they are challenging to secure, and hackers often target anyone they can find to use for malicious purposes. Likewise, email providers like Gmail and Outlook tend to block messages coming from custom servers. It'll take time to build enough reputation for news from your server to arrive in the recipient's inbox instead of spam folders.


In the world of email, two primary protocols facilitate the sending, receiving, and managing of messages: Simple Mail Transfer Protocol (SMTP) and Internet Message Access Protocol (IMAP). This article delves into the differences between these two protocols, their roles in email management, and their respective advantages and disadvantages.

SMTP: Simple Mail Transfer Protocol

SMTP is a protocol used for sending email messages between servers. It transmits messages from the sender to the recipient's email server. This protocol operates on a simple command-response mechanism, where the sending server issues a series of commands to the recipient's server to ensure that the message is delivered correctly.

Advantages of SMTP:

1. Reliability: SMTP uses a store-and-forward mechanism to ensure messages are delivered even during temporary network issues or server downtime. This means that if the recipient's server is unavailable, the message will be stored on the sending server until the recipient's server is back online.
2. Security: SMTP can be combined with Transport Layer Security (TLS) or Secure Sockets Layer (SSL) to encrypt email message transmission, ensuring the communication's privacy and security.
3. Scalability: SMTP is designed to handle large volumes of email messages, making it ideal for large organizations and email service providers.

Disadvantages of SMTP:

1. One-way communication: SMTP is a send-only protocol that cannot be used to retrieve or manage email messages on the server.
2. Lack of synchronization: Since SMTP does not support synchronization between devices, changes made to messages on one device are not reflected on others.

IMAP: Internet Message Access Protocol

IMAP is a protocol for receiving and managing email messages on an email server. Unlike SMTP, which is only concerned with sending messages, IMAP allows users to access, organize, and manage their email on the server. This means messages can be read, deleted, or marked as read on multiple devices, with the changes being synchronized across all devices.

Advantages of IMAP:

1. Synchronization: IMAP supports real-time synchronization across multiple devices, ensuring that actions taken on one device are immediately reflected on others.
2. Server-side storage: With IMAP, email messages are stored on the server, allowing users to access their email from any device with an internet connection. This also means that the notes are safe on the server in case of device failure.
3. Partial retrieval: IMAP allows users to retrieve only parts of an email, such as the message header or a specific attachment, without downloading the entire message. This can save bandwidth and improve performance on slow connections.

Disadvantages of IMAP:

1. Server dependency: IMAP relies on a constant connection to the server, which means that users may not be able to access their email if the server goes down.
2. Storage limits: Since IMAP stores messages on the server, users may face storage limits imposed by their email service provider.

In conclusion, both SMTP and IMAP play crucial roles in email communication. SMTP is responsible for sending messages between servers, while IMAP is designed for receiving and managing messages on the server. Each protocol has advantages and disadvantages, but they enable a seamless and efficient email experience for users. Understanding the differences between these two protocols can help businesses make informed decisions when choosing email service providers and configuring their email systems.

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