SMTP vs IMAP – What’s the Difference between these Email Protocols?

SMTP vs IMAP – What’s the Difference between these Email Protocols? There is a major difference between the two protocols that are involved in transferring electronic messages. In this article we we learn what SMTP email protocol is and then introduce IMAP and do a detailed comparison of them both.

What is a Protocol?

Protocols are involved when communicating through electronic devices. They are a set of standardized rules applicable to these types of communication methods. It is convenient when two devices communicate with the same protocol and the communication can also be done effectively.

TCP/IP, Hypertext Transfer Protocol (HTTP), User Datagram Protocol (UDP), File Transfer Protocol (FTP), Internet Message Access Protocol (IMAP) and Simple Mail Transfer Protocol (SMTP) are a few of the widely used communication protocols.

There are three main protocols used in email communication as the following, and most browsers support them.

  • Simple Mail Transfer Protocol (SMTP)
  • Internet Message Access Protocol (IMAP)
  • Post Office Protocol (POP).


In this article SMTP vs. IMAP we will discuss the differences between SMTP and IMAP protocols.

Email communication

There are three main parties involved in the email communication flow, as listed below.


  1. Sender – the person who initiates the email 
  2. Recipient  – the persons who receive the mail
  3. Mail server – the middle entity which is responsible for receiving and routing the email

When a sender sends an email, it directly goes to the email server. Then the email server helps the recipient to receive the specific email. Once you have successfully implemented the connectivity, the next critical thing is the email protocol, as it defines the standard of the connectivity.

What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. Mainly used for sending out email from an email client to an email server. It is the recommended industry standard protocol among all email protocols. This protocol is used after the email is drafted and you give the command to send it. SMTP server is basically used for setting up communication rules between servers.

There are two types of SMTP servers that are involved in communication. They are Relays and Receivers. Relays are used to accept and route a specific email from the sender to its recipient. Meanwhile, the receiver is the server who delivers that mail to the mailbox of the recipient after accepting it from relays. it is vital to mention that it functions between servers for the transfer of information.

SMTP servers can also be configured to be used as email gateways. SMTP users can provide instructions to the SMTP server on how the email transfer should be done.

SMTP communication is completed under three main stages.


  1. SMTP handshake – This is where the SMTP client connects with the respected SMTP server
  2. Email Transfer – Release the email
  3. Termination – The client-server communication is concluded here.

In the next section about SMTP vs IMAP – What’s the Difference between these Email Protocols? we will introduce IMAP email protocol.

SMTP features

  • Used for “Mail Relaying”.
  • SMTP supports multiple methods of communication. For example, you can send audios, videos, other media files and single messages to multiple clients.
  • One interesting feature of SMTP is its error handling capabilities. It successfully responds to an error request by taking the necessary actions.
  • It provides certain conditions for mail forwarding.
  • SMTP servers can be configured as email gateway.

What is IMAP?

IMAP stands for Internet Access Message Protocol. It is also known as the Interim mail access protocol, Interactive mail access protocol and Internet mail access protocol. This protocol simply manages the emails and looks into retrieving the emails from the servers. IMAP will not be useful in sending emails as it is involved in retrieving emails. However, it is the most commonly used protocol in retrieving emails.

IMAP manages multiple mailboxes and organize them into several categories.  Secondly, it helps track messages by assigning a flag to identify the seen messages. Thirdly, IMAP can identify which mails to be retrieved before downloading them into the mail server.  Fourthly, it keeps the emails on a remote email server, limiting the mailbox size. Therefore using IMAP if you need to keep copies of a large number of emails is not advised. However, you can always upgrade the storage as it is a limitation from the mail server side. Interestingly it only works between client and server for communication.

The flow of the IMAP is as follows.


  1. The recipient email client connects to the server where the message is located.
  2. The recipient can see the message headers on the server.
  3. Once you get a success response from the SPTP transmission, the email client of the receiver will get the message using IMAP and save it in the recipient’s inbox.
  4. When the receiver selects the exact message and starts reading it, IMAP downloads it for the receiver.

IMAP features

  • The main advantage of IMAP is that it allows receiving emails on more than a single device. So multiple mailboxes organized into various categories. So you can check it from any of your devices after successful login.
  • Furthermore, you can easily download multiple media files with IMAP. On the other hand, you cannot download the whole message if you haven’t opened it. It is beneficial for having a robust startup process.
  • IMAP is ideal if you need to access emails from different locations and your mailboxes are managed by multiple users.
  • Provides flags to keep track of which messages are being seen.
  • Another benefit is that it is capable of deciding whether to retrieve email from a mail server before downloading.
  • It is easy to download media when multiple files are attached.

One disadvantage of this mechanism is that it will not be properly executed when the internet connection is not good, making you unable to read the emails.

Next section about SMTP vs IMAP – What’s the Difference between these Email Protocols? we will compare both solutions. 

SMTP vs IMAP What’s the Difference?


SMTP vs IMAP, well the main difference between SMTP and IMAP is that both are meant for different functions. 

  • SMTP stands for Simple Mail Transfer Protocol while IMAP stands for Internet Access Message Protocol.
  • SMTP is only used for sending messages, while IMAP is used for managing and retrieving messages. Moreover, IMAP cannot be used for sending messages.
  • SMTP can be used to transfer messages between a client and server and also between two servers. But IMAP only supports transferring messages from a server to a client.
  • SMTP allows you to organize emails on the client storage, while IMAP users have the flexibility in organizing mail on servers.
  • SMTP works on port 25 (the standard port used for mail transferring), port 587 ( TLS encrypted port), port 465 (non-compliant port with RFC. This port can be used when you need to send secure messages with SMTP) and port 2525 ( Even though this port is not a standard port, it is commonly used by any email service. It can be used when you need to send non encrypted emails. On the other hand IMAP operates on port 993 (secured TLS/SSL port) which is used to have secured connectivity. It is also known as IMAPS and port 143 (it is the default port for IMAP).
  • IMAP offers much flexibility to the users and access through multiple devices, while SMTP allows changing emails after sending them successfully.

SMTP vs IMAP What’s the Difference between these Email Protocols? Conclusion

What did we learn about SMTP vs IMAP – What’s the Difference between these Email Protocols?

SMTP and IMAP are two main TCP/IP protocols that are widely being used.  It is best not to use them separately. What is more, they work altogether in sending and retrieving messages/emails by establishing the connectivity between sender, receiver and the email servers.

Email flow

  1. Create the email and click on send. The email client will send the mail to the respected email server using SMTP.
  2. The email server uses SMTP to send the message to the receiver’s email server.
  3. Once you get a success response from the second step, IMAP is used to fetch the email from the email client and save it in the email box for further reference.

SMTP is the industry standard protocol for sending email. So you that solution instead of IMAP, as that is  SMTP main function. IMAP on the other hand is the most common protocols for receiving email. Interestingly, IMAP syncs messages across all devices.


To summarize IMAP is best solution for anytime and anywhere access and when users need to access their mailboxes from multiple devices. In general use both protocols for a complete solution.


We hope it will be easier for you to identify when, where, and how to use SMTP and IMAP.

Avatar for Shanika Wickramasinghe
Shanika Wickramasinghe

Senior Software Engineer at WSO2 which is the 6th largest Open Source Software Company in the World. My main skills are machine learning and software development. I have 5+ years of experience as a Software engineer.

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