Mailer-Daemon

Mailer Daemon is a notification of a failed email delivery in the standard SMTP protocol.  This message may also be referred to as a bounce message or a Non-Delivery Report (NDR), Non-Delivery Notification (NDN) or a Delivery Status Notification (DSN) notification.  These notifications are automated email messages from a mail system that informs the sender of their message’s delivery problem — that the original sent message has bounced.

Bounced messages may occur at multiple points in the email’s delivery process. A sender may receive a mailer-daemon message from either the sender’s mail server or the recipient’s mail server. However, these notification messages are required when the bounce occurs on the recipient’s server: when a server essentially accepts the responsibility of delivering a message, it also accepts responsibility of notifying the sender if the message cannot be delivered.

These mailer-daemon notifications will include several pieces of pertinent information.  These details include the date and time at which the message bounced, the identity of the mail server that bounced the message and the reason that the message was bounced.

Mailer-daemon messages — and bounced messages — can result from a number of problems. Often, the recipient address is misspelled, or the address simply does not exist on the server. The address may also be experiencing resource exhaustion and have no remaining disk space to receive email communications.