So earlier today I went to help an old lady with some computer issues she told me she has been having. I try to be a good neighbor when I get opportunities to do stuff like that. She's in her mid-80s and has figured out a lot on her own.
When I got there, she had a list of ten things she wanted fixed on her computer. They were things like "when I type emails, for some reason they delete lines of text or close themselves." I had her type up an email and figured out that her wrists keep brushing the touchpad of her laptop when she types. She has a wireless mouse so I disabled the touchpad for her.
One of her problems towards the end of the list was that this guy kept harassing her via email and blocked her emails from going through. We looked in her inbox and she showed me a few messages from the mailer-daemon. I was about to explain what was going on but she wasn't done explaining the problem and how much of a jerk this guy was so I continued to listen.
Apparently this mailer-daemon guy blocked her emails any time she wanted to send something out to her daughter. She was very frustrated and had sent him six emails in response begging him to let her emails through. She let me read them. I really wish I had a copy of all six. Basically she called the mailer-daemon out for being a jerk, for not delivering her email, for taking advantage of a poor, old lady, and for depriving her daughter of the autobiography she was trying to send as an attachment. (She was also very worried that the mailer-daemon jerk had a copy of her autobiography now and could potentially publish it before she did). The last email she sent even threatened the mailer-daemon with the wrath of a just god who always protected old ladies.
At this point I had to stop her. I was able to keep a straight face somehow. I explained that the mailer-daemon wasn't a person. The mailer-daemon is just an automated response tool that sends you an email when it can't reach the email address you were trying to send to. I asked her if she was 100% certain that her daughter's email address was correct. She was. I then sent a test email from her email account to mine. It went through fine with no mailer-daemon response. At this point I asked her if she would call her daughter and ask her for her email address. After a while, I finally convinced her that the only possible option left was that the email address we were sending to was wrong. She called her daughter and found out that her daughter did have a different email address and had never even had one through comcast (where we were trying to send to). We finally got her autobiography through to her daughter, who confirmed over the phone that she had received it.
So after a good laugh, (I know... I'm a bad person) I decided to look up the origin of mailer-daemons. Apparently daemon comes from demon when its defined as "a useful and helpful spirit." You can look into the full origin of the term here