Mailer daemon

A mailer daemon!

A mailer daemon, also known as a mail daemon or mail server, is a computer program that handles the sending and receiving of email messages. It is a critical component of the email infrastructure, responsible for routing, storing, and delivering email messages between mail servers and users.

Here's how it works:

  1. Mail submission: When a user sends an email using a mail client (e.g., Outlook, Gmail), the email is submitted to the mailer daemon on the user's mail server.
  2. Mail processing: The mailer daemon processes the email, checking for errors, formatting the message, and adding headers (e.g., From, To, Subject).
  3. Mail routing: The mailer daemon determines the destination mail server for the email and routes it accordingly. This may involve looking up the recipient's email address in a database or using a DNS (Domain Name System) lookup to determine the recipient's mail server.
  4. Mail storage: If the mailer daemon cannot deliver the email immediately (e.g., because the recipient's mail server is down), it stores the email in a queue for later delivery.
  5. Mail delivery: When the recipient's mail server is available, the mailer daemon delivers the email to the recipient's mailbox.

Some common mailer daemons include:

  1. Postfix: A popular open-source mail server developed by IBM.
  2. Sendmail: A widely used mail server developed by Eric Allman.
  3. Exim: A free and open-source mail server developed by the University of Cambridge.
  4. Qmail: A secure and reliable mail server developed by Dan Bernstein.

Mailer daemons are essential for the functioning of the internet, as they enable email communication between individuals and organizations worldwide.