Mailer daemon
A mailer daemon is a software program that runs in the background on a computer or network device, responsible for managing and processing email messages. The term "daemon" comes from the Greek word "daimon," meaning "spirit" or "servant," and refers to a program that runs in the background, performing tasks without direct user interaction.
A mailer daemon typically performs the following functions:
- Receiving and processing email: The daemon receives email messages from the internet or other email servers, and processes them according to the email protocol (e.g., SMTP, POP3, IMAP).
- Storing email: The daemon stores email messages in a mailbox or email database, allowing users to access and manage their email accounts.
- Delivering email: The daemon delivers email messages to the intended recipients, either locally or remotely, using the email protocol.
- Managing email queues: The daemon manages email queues, which are lists of email messages waiting to be processed or delivered.
- Error handling: The daemon handles errors and exceptions that occur during email processing, such as bounced messages or delivery failures.
Examples of mailer daemons include:
- Postfix: A popular open-source mail transfer agent (MTA) used on Linux and Unix systems.
- Sendmail: A widely used MTA developed by Larry Roberts and Eric Allman in the 1970s.
- Exim: A free and open-source MTA developed by the University of Cambridge.
- Qmail: A secure and reliable MTA developed by Dan Bernstein.
- Microsoft Exchange: A proprietary email server software developed by Microsoft.
Mailer daemons are essential for email communication, as they enable email servers to exchange messages and deliver them to users' email accounts.