What Is an Email Server?

April 26, 2024

Email servers are critical systems that ensure that emails are delivered securely from sender to recipient. They also handle many other tasks, from filtering spam to storing messages for future access, making them integral to both personal and professional contexts.

What Is an Email Server?

An email server is a computer system that sends and receives email over the internet. It acts as a post office, handling the complex process of message transmission by using standard email protocols such as SMTP for sending messages and POP3 or IMAP for receiving them.

The server ensures that emails are correctly routed from the sender’s email client to the recipient's email client, verifying the users and managing the storage of email messages until they are deleted or archived. Beyond mere transmission, email servers are equipped with functionalities to secure communications, filter out unwanted spam, and manage the massive volumes of digital correspondence that individuals and organizations exchange daily.

Email Server vs. Email Client

An email server is the system that manages the transmission and storage of email messages over the network. It acts as a central hub, facilitating the send and receive processes using standardized protocols like SMTP, POP3, and IMAP.

The server's main role is correct route and deliver messages between senders and recipients, regardless of their location. It also provides essential services such as security measures to protect against unauthorized access, spam filtering to prevent unwanted emails, and the maintenance of message history and backups. Essentially, the email server acts as the backbone of email communication, managing the flow and integrity of email data.

In contrast, an email client is an application used by individuals to interact with the email server, allowing them to send, receive, and organize their emails in a user-friendly interface. Email clients can be web-based, like Gmail or Yahoo Mail, or desktop-based, such as Microsoft Outlook or Mozilla Thunderbird.

The primary function of an email client is to provide users with a convenient way to access their emails stored on the server, compose new messages, and manage their personal email accounts. It acts as the face of email communication, translating the technical processes managed by the server into an accessible and manageable format for everyday use.

How Does an Email Server Work?

An email server facilitates the sending and receiving of emails using a series of well-defined steps and protocols. Here's how it typically works:

Sending an Email

  1. Compose. The process begins when a user composes an email using an email client. This client can be either a web-based interface or a desktop application.
  2. Connect to server. Once the email is ready to be sent, the email client connects to the email server using the Simple Mail Transfer Protocol (SMTP). The client submits the email along with the recipient's address to the server.
  3. Authentication. The server then verifies the sender’s credentials (username and password) to authenticate the request. This step ensures that the sender is permitted to use the server for email transmission.
  4. Lookup and routing. Next, the server looks up the domain of the recipient’s email address in the Domain Name System (DNS) to find the corresponding recipient server. Once identified, it forwards the email to the recipient’s email server.

Receiving an Email

  1. Receipt by recipient’s server. The recipient's email server receives the message and processes it. This server also uses SMTP to receive messages but employs additional protocols like Post Office Protocol version 3 (POP3) or Internet Message Access Protocol (IMAP) for email retrieval by the client.
  2. Storage. Upon receipt, the email is stored in a mailbox on the recipient’s server until the recipient accesses it.
  3. Access by recipient. When the recipient opens their email client, the client contacts the server to download new mail. If using IMAP, the email can be viewed directly on the server, allowing synchronization across multiple devices. With POP3, emails are typically downloaded and possibly removed from the server, depending on the client settings.

Additional Functions

  1. Spam and security filters. As emails are processed, both incoming and outgoing messages are checked by the server for spam and malicious content, using various filters and scanning software to protect users.
  2. Backups and archives. Email servers often include functionality to backup and archive emails, ensuring data integrity and compliance with data retention policies.

Email Server Protocols

Email servers use several protocols to handle different aspects of email transmission and reception. Each protocol serves a unique function, facilitating smooth communication over the internet. Here's a breakdown of the major email server protocols.

Simple Mail Transfer Protocol (SMTP)

SMTP is used to send and route emails between servers. Email clients also employ it to send outgoing messages to a server. When you send an email, your email client communicates with the email server using SMTP. The server then uses SMTP to relay this message to the recipient's email server. SMTP handles the connection between servers but doesn't deal with downloading emails to the user's device.

Post Office Protocol version 3 (POP3)

POP3 retrieves emails from the server to the user's device. It is designed to support offline email processing. When using POP3, the email client connects to the email server to download all new messages to the local device (such as a computer or smartphone). Once downloaded, the messages are typically deleted from the server, although settings can be adjusted to leave a copy on the server for a specified time.

Internet Message Access Protocol (IMAP)

IMAP is used to retrieve emails and manage mailboxes from multiple devices. IMAP synchronizes the email client with the server. When you read, delete, or organize your emails in the client, the same actions are mirrored on the server in real time. This means you can access your email from any device with an internet connection, and your mailbox will look the same everywhere.

Secure Sockets Layer (SSL) and Transport Layer Security (TLS)

SSL and TLS are protocols used to encrypt the connection between email clients and servers. This ensures that all data exchanged remains confidential and secure from eavesdropping. When an email client connects to an email server, SSL/TLS ensures the connection is encrypted. This security measure is crucial, especially when transmitting sensitive information over potentially insecure networks.

Email Server Benefits

Email servers offer a range of benefits that streamline communication and enhance productivity for both individuals and organizations. Here are some key advantages:

  • Centralized management. Email servers provide a centralized platform for managing email communications, making it easier for organizations to control and oversee operations, including email security, backups, and archiving. Centralized management also facilitates easier maintenance and updates, ensuring that the email system operates smoothly and efficiently.
  • Security features. Robust security measures are a fundamental aspect of email servers. They offer features like encryption, spam filtering, and virus scanning to protect sensitive information from unauthorized access and cyber attacks.
  • Scalability. Email servers are designed to handle varying volumes of email traffic. As an organization grows, the server can be scaled to accommodate increased demands without compromising performance.
  • Accessibility and synchronization. Modern email servers support protocols like IMAP, which allow for real-time synchronization across multiple devices. Users can access their email from anywhere, using any device, and see the same mailbox content consistently.
  • Data integrity and backup. Email servers often include automatic backup systems that help preserve data integrity. In the event of hardware failure, data corruption, or other issues, these backups can be used to restore lost or damaged emails. This feature is essential for businesses that need to ensure data is not lost and can comply with data retention laws and regulations.
  • Customization and control. Owning and managing an email server allows organizations to customize settings, configurations, and policies to meet specific needs. This control over the email environment enables businesses to implement custom workflows, compliance measures, and integration with other internal systems.

Anastazija is an experienced content writer with knowledge and passion for cloud computing, information technology, and online security. At phoenixNAP, she focuses on answering burning questions about ensuring data robustness and security for all participants in the digital landscape.