What is a Mail Server?

A mail server (also known as an email server) is a software application that handles the sending, receiving, and storage of emails. 


Mail servers are crucial for the email delivery process. They ensure that email messages are efficiently routed from the sender to the recipient


Mail servers operate based on standardized email protocols and are responsible for ensuring the smooth transfer of emails between apps and servers across the internet.



What Does a Mail Server Include?

A Mail Server consists of several components which work together to send and receive email messages, these include: 

  1. SMTP (Simple Mail Transfer Protocol) Server

    The SMTP server sends outgoing emails from the sender’s app to the recipient’s email server. It handles the routing and delivery of messages, ensuring they reach the correct destination.

    Key functions include:


    • Email Submission: Accepts emails from the sender’s email app.


    • Email Relaying: Forward emails to other mail servers if the recipient’s server differs from the sender’s.



  2. IMAP (Internet Message Access Protocol)

    The IMAP server manages incoming emails and allows users to access and manage their email messages on the mail server without downloading them to their local devices. 


    Key features include:


    • Email Synchronization: Keeps emails synchronized across multiple devices.



    • Partial Fetch: Allows partial download of email content, improving efficiency.


  3. POP3 (Post Office Protocol 3) Server

    The POP3 server is another (older) protocol for receiving emails. Unlike IMAP, it downloads emails from the mail server to the local device and typically deletes them from the server. Key characteristics include:


    • Email Download: Downloads entire emails to the user’s device.


    • Single Device Access: Best suited for accessing email from a single device.


    • Offline Access: Emails are available offline once downloaded.


  4. Mail Transfer Agent (MTA)

    The MTA is software that transfers emails between servers. It works with SMTP to route and deliver emails. Popular MTAs include Postfix, Sendmail, and Exim.

  5. Mail Delivery Agent (MDA)

    The MDA is responsible for delivering emails to the recipient’s inbox. It works with the MTA and email protocols to ensure proper delivery. Examples include Dovecot and Procmail.

  6. Mail User Agent (MUA)

    The MUA is the email app used by users to send, receive, and manage emails. Examples include Spike, Microsoft Outlook, Gmail, and Apple Mail.



How Do Mail Servers Send & Receive Emails?

Email Sending Process


When a user sends an email, the email client (MUA) connects to the SMTP server, relaying the email through the internet to the recipient’s mail server. The recipient’s mail server stores the email until the recipient retrieves it using an email client via IMAP or POP3.


Email Receiving Process


The recipient’s email app connects to the mail server using IMAP or POP3 to retrieve the email. IMAP lets the user view and manage emails directly on the server, while POP3 downloads the emails to the local device.



Additional Uses for Mail Servers

  1. Data Management

    Mail servers store and manage vast amounts of email data, ensuring users can access their messages whenever needed. They provide organized storage and retrieval systems.

  2. Email Security

    Mail servers implement various security measures, such as encryption, authentication, and spam filtering, to protect email communication from unauthorized access and cyber threats.

  3. Scalability

    Mail servers can handle large volumes of email traffic, making them suitable for small and large businesses. They can scale to accommodate growing communication needs.



5 Popular Mail Servers

  1. Microsoft Exchange Server

    Microsoft Exchange Server is a widely used mail server solution that offers robust email management, calendaring, and collaboration features. It integrates seamlessly with Microsoft Outlook and the ActiveSync protocol.

  2. Postfix

    Postfix is an open-source mail transfer agent (MTA) known for its performance and security. It is widely used on Unix-based systems.

  3. Sendmail

    Sendmail is one of the oldest and most widely used MTAs. It is known for its flexibility and extensive configuration options.

  4. Dovecot

    Dovecot is an open-source IMAP and POP3 server known for its security and performance. It is often used in conjunction with other MTAs like Postfix.

  5. Exim

    Exim is an open-source MTA that is highly configurable and widely used on Unix-based systems. It is known for its flexibility and robustness.

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