mail daemon
Mail Daemon or Mailer Daemon or also called Bounce Message or Bounce E-Mail is the error message in case of undeliverable e-mails. It is automatically generated by the mail server and sent to the sender of the e-mail. He receives the Delivery Status Notification, which often informs about the reason of undeliverability. Examples of undeliverability are User Unknown, Host Unknown, Mailbox not Found or Mailbox Full.
A distinction is made between hardbounces and softbounces. Hardbounces are returns due to permanent errors, which occur, for example, with incorrect, invalid or non-existent e-mail addresses. Softbounces occur when the e-mail system is temporarily unavailable or when the mailbox is full and there are therefore temporary reasons for non-delivery.
Bounce emails can be reduced by programs that send out emails according to a mailing list. Since these programs perform certain actions, the mail daemons resend after a certain time or remove the undeliverable email addresses from the mailing list.