"Mailer-Daemon"/Message undeliverable error in a returning Email - what does it mean?

The mailer daemon is the program that is responsible for delivering e-mails when they are sent. If delivery is not possible for some reason, this program sends a notification to the sender of the mail. Mailer-daemon @ (sender's server) is often specified as the sender of the notification.

This error message can have various causes which are mentioned in the mail itself. Here are some examples:

• "unknown user" – the email address is incorrect or maybe misspelled
• "Mailbox quota exceedet" – the recipient's mailbox is full
• "could not send message for 4 hours" – a warning that the recipient's mail server was not immediately available
• "unrouteable domain ’xxx.de’" – the part of the email address after the "@" may be misspelled.
• Remote server replied: 550 52.157.149.216 is not allowed to send mail from yourdomain.com: You must set the authorization on your e-mail server so that eTermin (IP 52.157.149.216) can send e-mails via your server.

Please analyze the error message carefully. This can be used to identify the cause and, if necessary, to derive a solution (e.g. correcting a misspelled e-mail address). If you cannot derive a solution, please contact your e-mail provider.