What is a Mail Server? POP3, IMAP, AND SMTP Simply Explained

Written By Ananaya Kandpal

Published On January 28, 2026

Reading time: 4 minutes

The term mail server refers to a crucial component of the email infrastructure, responsible for sending, receiving, and storing email messages. It works like an intermediary between email clients, such as Gmail, Outlook, or Thunderbird, and certifies that emails are delivered to the correct recipients. This post is going to explain what a mail server is, its types, examples, and the popular software used to manage email communication.

A mail server, also called an email server, is a computer system or application that handles and stores email. It allows the exchange of messages over a network by using specific protocols to manage the sending, receiving, and storing of emails. In a nutshell, a mail server acts as a digital post office where emails are processed and delivered to the right destinations.

How does a mail server work?

Mail servers operate using a client-server model, which consists of sending and receiving emails using different protocols.

• Email Creation: The user composes an email using an email client, such as Gmail or Outlook.

• SMTP Protocol: The email client sends the message to the mail server by using SMTP, Simple Mail Transfer Protocol, which transfers the email to the recipient’s mail server.

• Mail Server Storage: The recipient’s mail server receives the email and stores it until the user retrieves it.

• IMAP or POP3 Protocols: The recipient’s email client accesses the email through IMAP, Internet Message Access Protocol, or POP3, Post Office Protocol 3, to download or view the message.

Types of Mail Server Protocols Explained

SMTP (Simple Mail Transfer Protocol)

SMTP is responsible for sending emails. Whenever you click “Send” in your email client, SMTP comes into action. It transfers the email from your device to your outgoing mail server and then forwards it to the recipient's mail server.

SMTP does not store emails or allow users to retrieve them. Its only job is to ensure that messages are routed correctly between mail servers. Without SMTP, email communication would simply not exist.

POP3 (Post Office Protocol 3)

POP3 is a protocol used for retrieving emails from a mail server. When you connect your email client using POP3, the messages are downloaded from the server to your device.

In most cases, POP3 removes emails from the server after download. This means your emails are stored locally on one device, making POP3 suitable for users who access email from a single system and want offline access.

However, this also means that emails may not sync across multiple devices, which can be a limitation for modern users.

IMAP (Internet Message Access Protocol)

IMAP is a more advanced protocol used for accessing and managing emails directly on the server. Instead of downloading messages permanently, IMAP keeps emails stored on the mail server and syncs them across all connected devices.

This allows users to check emails from multiple devices, such as laptops, smartphones, or tablets, while keeping everything consistent. Actions like reading, deleting, or organizing emails are reflected everywhere.

Types of Mail Servers

Mail servers can be classified based on their role in email communication:

• Incoming Mail Servers: These handle incoming messages and store them until users access them via IMAP or POP3.

• Outgoing Mail Servers: These use SMTP to send emails to recipient servers.

• Dedicated Mail Servers: Designed exclusively for email services, offering better security, performance, and control.

• Cloud-Based Mail Servers: Hosted on cloud infrastructure, offering scalability, redundancy, and high availability.

Common Examples of Mail Servers

Many popular email services rely on powerful mail server infrastructures, including:

• Gmail

• Microsoft Outlook / Exchange

• Yahoo Mail

• Zoho Mail

• Zimbra Email Server

Why Mail Servers Are Important for Businesses?

Mail servers play a vital role in professional communication. A reliable mail server ensures:

• Secure email delivery

• Reduced spam and phishing risks

• Better control over data and storage

• High uptime and consistent performance

• Professional brand identity with domain-based email

Thus, a mail server is indeed the backbone of email communication. From sending messages using SMTP to retrieving them through IMAP or OP3, each email interaction relies on a properly configured mail server.

Understanding how mail servers work assists individuals and businesses in selecting the right email hosting Services, troubleshooting common issues, and maintaining secure, reliable communication.

Whether you are handling personal email or operating a business email system, knowing the basics of mail servers and protocols is crucial for smooth and effective email operations.