What's a mail server

A mail server is a computer system that handles email messages and routes them to their intended recipients. It's a crucial component of the email infrastructure, allowing users to send and receive emails.

A mail server typically performs the following functions:

  1. Receiving emails: It accepts incoming emails from other mail servers or users and stores them in a database.
  2. Storing emails: It stores emails in a database or file system, often organized by user or domain.
  3. Routing emails: It routes emails to their intended recipients, either by delivering them directly to the recipient's email client or by forwarding them to another mail server.
  4. Delivering emails: It delivers emails to the recipient's email client, such as Microsoft Outlook, Mozilla Thunderbird, or a web-based email client like Gmail.
  5. Managing email accounts: It manages email accounts, including creating, deleting, and modifying user accounts, as well as setting up email forwarding and autoresponders.
  6. Spam and virus filtering: It filters out spam and viruses from incoming emails to prevent them from reaching users' inboxes.
  7. Backup and recovery: It provides backup and recovery mechanisms to ensure that emails are not lost in case of a system failure or data corruption.

Mail servers can be categorized into two main types:

  1. Mail Transfer Agent (MTA): An MTA is responsible for transferring emails between mail servers. Examples of MTAs include Postfix, Sendmail, and Exim.
  2. Mail Delivery Agent (MDA): An MDA is responsible for delivering emails to users' email clients. Examples of MDAs include Procmail and Fetchmail.

Some common mail server protocols include:

  1. SMTP (Simple Mail Transfer Protocol): Used for sending and receiving emails between mail servers.
  2. POP3 (Post Office Protocol version 3): Used for retrieving emails from a mail server to a user's email client.
  3. IMAP (Internet Message Access Protocol): Used for retrieving and managing emails on a mail server.

Mail servers can be hosted on-premises or in the cloud, and they can be managed manually or using automation tools.