Email Protocols Explained: IMAP vs POP3 vs SMTP [2024]

Three main parties are involved in transferring an electronic message: the sender, the recipient, and the gmail server. The gmail goes from the sender to lớn the mail server, which then lets the recipient get the message. 

What is the role of gmail protocols here? They establish connections between transferring parties. So, one protocol is needed to lớn send, and one – to lớn receive. 

Today, we’ll review and compare the three most commonly used gmail protocols – IMAP vs POP3 vs SMTP – and help you choose the right option for your needs. 

What is an gmail protocol? 

An gmail protocol is a combination of principles and rules that make it possible to lớn transfer messages between different servers, machines, and gmail clients. It creates standards that messages should follow to lớn reach the recipients in their original state. 

For example, when you send an gmail from Gmail client to lớn someone with Outlook address, you expect all the attachments and body toàn thân elements to lớn be present when they view your gmail. This is true whether they use Apple Mail, Microsoft Outlook, or Thunderbird clients to lớn access their inbox. 

Email protocols also determine how messages should be sent and accessed, what format they should have, and what structure should the connection follow. 

SMTP – a standard protocol to lớn send emails

What is SMTP?

Simple Mail Transfer Protocol (SMTP) establishes how the message gets from the sender to lớn the gmail server. Also, it is used by a mail transfer agent (MTA) to lớn deliver emails between servers. This process is called mail relaying (or SMTP relay). 

SMTP is only meant for sending gmail messages. 

How SMTP works

SMTP workflow consists of commands sent by the SMTP client and corresponding replies by the SMTP server. 

Default SMTP commands are text-based, such as HELO, MAIL FROM, and others. Sometimes you might encounter extended SMTP (ESMTP) commands such as EHLO, STARTTLS, etc. 

Replies are represented by numeric completion codes (for example, 220, 250, 354, and ví on). For more on SMTP commands and response codes, read our dedicated blog post.

Any SMTP conversation consists of three stages:

• SMTP handshake – The SMTP client establishes a TCP connection with the SMTP server. Once the server replies with 250, the handshaking starts. The stage ends when the server confirms the recipient’s address.
• Email transfer – Code 354, as a response to lớn the DATA command, launches the transfer of the gmail. Once the server gets a final dot, the message is transferred. 
• Termination – Client and server say goodbye to lớn each other using the command QUIT and code 221, respectively. 

Let’s take a look at the interaction between the SMTP client and server through a simple gmail delivery example:

SMTP ports

• 25

This is a standard port for relaying messages between gmail servers. Cloud hosting providers and many gmail clients (Gmail, Microsoft Outlook, Mozilla Thunderbird, etc.) block port 25 to lớn prevent spam. They usually prioritize secure connections lượt thích 587 or 465.

• 465

465 is not an RFC-compliant port. It was meant for the SMTPS encryption and authentication wrapper over SMTP. IANA registered 465 as an SMTP port, but it has never been recognized as an official SMTP transmission or submission channel. 

Later on, port 465 became obsolete and was revoked in favor of STARTTLS wrapper over SMTP. Nevertheless, today many servers still use SMTPS and maintain 465.

• 587

A mặc định SMTP port 587 is the option to lớn submit an gmail for routing. TLS encryption ensures the secure submission of the gmail. Almost all mail servers tư vấn 587.

• 2525

It is not an official SMTP port, but almost any gmail service provider supports it. 2525 is secured similarly to lớn 587 and is often used in lieu of it. So, if the use of the mặc định SMTP port causes some trouble, try 2525.

For more on this, read our blog post about SMTP ports.

And for a deeper dive into the differences between SMTP and a protocol such as IMAP, kiểm tra out this video:

IMAP4 and POP3 – protocols to lớn receive emails

Once the gmail knocks at the mail server’s door, either IMAP or POP3 will be used to lớn retrieve it. Both of these servers are message accessing agents (MAAs). 

What is IMAP?

Internet Message Access Protocol (IMAP) is a communication standard for accessing emails. Today, its fourth version is in use, hence the name IMAP4. 

IMAP stores emails on a remote server and downloads them on demand when the recipient opens them. So, the IMAP protocol gets access to lớn the gmail from any device or location if authorized. This allows for gmail synchronization, which is why IMAP is the go-to option for most gmail service providers. 

How IMAP works

Here is the basic flow of the IMAP client/server interaction: 

• A recipient’s mail client connects to lớn the server the message is stored on
• The recipient can see the message headers of all the emails on the server
• If the recipient chooses a particular message to lớn read, IMAP downloads it on demand

Under the hood, a primitive IMAP connection may look as follows:

Here you’ll find a full selection of client commands.

Darn! We forgot about the IMAP server responses. There are three forms of them:

• Status Responses (OK, NO, BAD, PREAUTH, and BYE)

They may include a response code lượt thích ALERT or CAPABILITY.  A response code gives additional information beyond the status response condition. 

• Server Data

These responses include Server and Mailbox Status (CAPABILITY, LIST, etc.), Mailbox Size (EXISTS and RECENT), and Message Status (EXPUNGE and FETCH)

• Command Continuation Request

This response confirms that the server is ready to lớn accept the continuation of the client’s command. It is represented by a “+” token.

IMAP ports

• 143 – A mặc định IMAP port without encryption
• 993 – A secured SSL/TLS port used by most gmail service providers. It is often called IMAPS. 

What is POP3?

Post Office Protocol 3 is a simpler way to lớn access mailboxes. We use its third version – that’s why it’s called POP3. Users love this protocol for its low dependency on Internet connections. 

POP3 protocol downloads emails from the server to lớn the local computer, ví you can read them even offline. The server deletes messages once they are retrieved. This is the mặc định and common setting, but there is the option to lớn enforce a site policy regarding gmail retention on the server. 

At the same time, even if the POP3 client contains configuration options to lớn store gmail, the server won’t tư vấn such an action. 

How POP3 works

POP3 connection consists of four steps: 

• The client connects to lớn the server (AUTHORIZATION State)
• The client retrieves new emails (TRANSACTION State)
• The server deletes the stored messages (UPDATE State)
• The client disconnects from the server

Let’s take a look under the hood of a POP3 session as well. 

We used only two commands (DELE and STAT) that are valid in the TRANSACTION state. You can find more options here. 

As for POP3 responses, they contain a status indicator (+OK or -ERR) and a keywords that may be enhanced with additional information (for example, -ERR no such message, only 2 messages in maildrop).

POP3 ports

• 110 – A mặc định POP3 port without encryption
• 995 – A secured SSL/TLS port that is often referred to lớn as POP3S. 

IMAP or POP3 – which protocol should I choose? 

At first, we were considering making a table with a comparison of the pros and cons of IMAP and POP3. But this idea proved untenable since different users would have different demands in terms of the gmail protocol standards. So, we decided to lớn mix it up this way instead.

Pick IMAP4 if: 

• you need access to lớn mail from different devices 
• you need to lớn organize your mail in folders or some sort of hierarchy
• you have unlimited server storage space
• you have a constant and stable Internet connection
• you need fast access to lớn your mail

Pick POP3 if: 

• your mạng internet connection is unstable or even unavailable
• you prioritize privacy over accessibility and prefer to lớn store emails on the local machine
• you’re the only person with access to lớn your gmail tài khoản and use a single device for that purpose

If you still don’t know which protocol to lớn choose, kiểm tra out our article on the key differences between IMAP and POP3 or watch this video:

What about HTTP? 

HyperText Transfer Protocol (HHTP) is another option to lớn access emails, yet it’s not an gmail protocol. Regardless, HTTP can be used to lớn send and receive messages from webmail, such as Gmail.com. It’s also good practice to lớn access emails in mobile apps through HTTP. 

This protocol has two mặc định ports: 80 for non-encrypted and 443 for secure connections. 

How an gmail gets from a sender to lớn a recipient 

Now, you know what each gmail protocol is used for. Let’s map a full picture of how an electronic message can get from a sender ([email protected]) to lớn a recipient ([email protected]). 

• Sender’s gmail client connects to lớn the SMTP server (for example, smtp.gmail.com)
• The SMTP server authenticates the recipient’s gmail address using DNS records (for more information on gmail authentication, read our blog posts about SPF, DKIM, DMARC, and BIMIrecords or watch videos on our YouTube channel)
• Once the Gmail SMTP server authorizes the recipient, it sends the gmail to lớn the SMTP server of recipient.com
• Recipient.com’s SMTP server verifies whether [email protected] is valid
• The SMTP server forwards the gmail to lớn the IMAP/POP3 server

Is it enough to lớn mix up gmail protocols to lớn send and receive emails successfully?  

The short answer is no. While properly-set-up gmail protocols are essential, they are certainly not enough. You need a safe gmail infrastructure with built-in deliverability tools to lớn reach recipients’ inboxes.

To learn more about what an gmail infrastructure is, kiểm tra out our dedicated video:

Along with an gmail infrastructure, you may also need a virtual inbox to lớn receive all your test emails. 

Mailtrap is a single platform that takes care of all your email-related needs. Test your emails using a fake SMTP server provided by Thư điện tử Testing, send your emails with Thư điện tử Sending’s reliable SMTP server, and monitor the performance of your infrastructure. All of that within one Thư điện tử Delivery Platform. 

Email Testing is an Thư điện tử Sandbox that captures all your SMTP traffic. You can use it to lớn kiểm tra the gmail sending functionality of your tiện ích and see whether the SMTP server is configured properly. With Thư điện tử Testing’s HTML Check and Spam Analysis features, you’ll tackle deliverability issues before your tiện ích hits the production environment. 

Once you’re done with testing, you can configure your tiện ích to lớn use Thư điện tử Sending’s SMTP server that delivers your emails to lớn the inboxes in seconds. Alternatively, integrate Mailtrap with API for more flexibility. Whichever method you choose, you’ll get access to lớn Thư điện tử Sending’s unique monitoring capabilities – actionable analytics with drill-down reports and helicopter-view dashboards. 

Here’s what the gmail delivery flow will look lượt thích if you were to lớn use Mailtrap’s Thư điện tử Sending or Thư điện tử Testing: 

• Sender’s gmail client connects to lớn the real or fake SMTP server (live.smtp. and sandbox.smtp., respectively). Mailtrap provides all the required credentials lượt thích port, username, password, and authentication method. 
• If you’re using Thư điện tử Testing, the fake SMTP server will send an gmail to lớn the POP3 server (pop3.).
  • You’ll see your message in your Demo inbox if your tiện ích functions properly. 
• If you’re using Thư điện tử Sending, the emails will be directed to lớn the recipients’ POP3 or IMAP servers.
  • In a matter of seconds, they will pop up in your recipients’ inboxes. 

For more information on integrating and using Mailtrap, refer to lớn our getting started guide. 

We hope our blog post on IMAP vs POP3 vs SMTP helped clarify the complicated world of emails.