Who (what) is "MAILER-DAEMON" and why does he tell me the email addresses I sent email to do not work?

Mailer-Daemon is one of the most popular names among a large series of E-Mail Administration Programs. Is actually an automated "majordomo" that replies everytime an address is not recognized on an E-Mail Server, telling you that the address you used can not be located or that your message was not delivered, sometimes telling you a probable reason.

For instance, if you sent an email to "somebody@answerbag.com", and "somebody" is not an actual or valid E-mail User on the Answerbag E-Mail server then you will receive a reply notifying you that your E-mail message did not reach a user.

The most common names for the AutoReply mailer are: Mailer-Daemon, Postmaster, Majordomo, Mail-Admin, Mail-Administrator and the list goes on and on.

For general knowledge a "Daemon" is defined in Computer Science as "A program or process that sits idly in the background until it is invoked to perform its task". The word comes from the Greek "Daimon" (an inferior deity) that originated the English "Demon" (an evil demigod).

Mailer-daemon is email server software responsible for message delivery. Messages from mailer-daemon@example.com usually indicate a problem with the recipient's mail server or address. For example, a common problem that causes a mailer Daemon message is sending a message to an incorrect e-mail address. You may receive email bounce-back messages from mailer-daemon that were not yours to begin with, but unsolicited commercial email bounce-backs. If you send legitimate email to a valid account and still get responses back from mailer-daemon, your domain may be on a blacklist.

its a mail devil that messes up emails

This answer is not a real answer. I have been regularly sending emails to both of my daughters at their work addresses, they are valid, always have been, but suddenly for two days now, I often get the mailer-daemon message that they could not be delivered. this has to be wrong, there is nothing wrong with those addresses. so what is going on??

mailer demon is actually the e-mail company. for example if i have yahoo and i accidentally send an e-mail to a non-existing e-mail address mailer demon(aka yahoo) sends me an e-mail back telling me that the e-mail wasn't sent because its an invalid e-mail address. don't worry it isn't a virus or anything.

why does he tell me the e-mail doesn't work. when its a prison email??