Unfortunately it is not unusual to receive annoying emails at regular intervals from a strange email address that resembles firstname.lastname@example.org. This tutorial will walk you through how to avoid receiving this type of message.
An email from a postmaster is sent because there has been a failure during message delivery. The body of the email usually includes a message saying, "The following delivery to recipients failed." This can be caused for many reasons, including a crashed account, a problem with the mail server, a hacked account, or an incorrect email address.
If you have verified that the recipient's email address is correct and that you aren't experiencing any issues with your account or server, then you may need to protect yourself against potential hacking. You should change your password and clean your computer with software, like CCleaner.