small program in Unix that check for activity
Returns bounced mail. Makes sure that programs are supposed to run at certain times. Many mailer daemons tell exactly what the problem is. If the message starts with 550, it is an error message telling the user what went wrong with delivery.
A program associated with UNIX systems that performs a housekeeping or maintenance utility function without being called by the user. A daemon sits in the background and is activated only when needed, for example, to correct an error from which another program cannot recover.
Small programs in Unix that run frequently to see whether something has happened. If so, they act as they were programmed; if not, they go back to sleep.
Special small programs that perform specific tasks. A daemon may run all the time "watching" a system or they may "wake up" when a task needs to be performed. For example the program that wakes up to deliver a mail message, or a file to be printed. When a mail message cannot be delivered you may receive a message from the mailer daemon.