What Every Email Marketer Should Know About Mailer-Daemon Spam

When you send an email to a defunct address, the mailer-daemon responds that the message was not delivered. If your inbox becomes suddenly flooded with delivery failure reports, this could be the result of someone sending emails from your address without your permission.

Definition of Mailer-Daemon

Email functions similarly to a virtual postal system. When you send an email, the message is routed through a server called the mailer-daemon. This server forwards the message to additional servers until it reaches the recipient’s inbox. When delivery is not successful, a mailer-daemon error message is generated and returned to the sender.

Definition of Mailer-Daemon Spam

Mailer-daemons do not use the From line address to determine the sender of an email. Rather than that, a mailer-daemon makes use of the email header, which includes a return path with the sender’s address. Spammers can send messages that appear to be from you without gaining access to your account by forging your email address in the email header. If they send an email to an invalid address, you will receive mailer-daemon spam.

Because every email must include a sender in the From line and spammers are loathe to use their own, they frequently look up random addresses in people’s contacts to use for phishing and other nefarious purposes.

If you open an email that contains a virus or a worm, the virus or worm can infect your computer and spread to everyone in your address book. Receiving mailer-daemon spam does not always indicate the presence of malware, but there are some precautions to take.

What to Do If You Receive Mailer-Daemon Spam

When you receive mailer-daemon spam, the following steps should be taken:

  1. Perform a malware scan on your computer and mobile devices. When performing a malware scan on your computer, ensure that you are not connected to the internet. After that, change the passwords for all of your accounts.
  2. Report the mailer-daemon as spam. Most email programs include a feature that allows users to mark emails as spam. For instance, when you report spam in Gmail, the information contained in the email is used to prevent similar messages from being sent in the future.
  3. Inform your contacts. If you are receiving mailer-daemon spam, some of your contacts may have received infected emails from you. Notify everyone of the incident and instruct them to disregard any suspicious messages from your address.


Email servers employ measures to minimize the number of unnecessary delivery notifications sent. For instance, they might check to see if a return address has been forged prior to sending a delivery failure message. If the address is clearly not that of the intended recipient, no error email is sent.

Email servers that receive a high volume of delivery failures for an address (typically due to spam or malware content) may either delete the messages silently or quarantine them in your spam folder.

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