The actual cause can be either a worm virus (run immediately your anti-virus) or the so-called spoofing: a spammer pretending to be you employing your address name. What if you receive a “Mail Delivery Failure” notification for messages you did not send at all? It may well be that you’ve been under a malware attack: a virus is using your account to send spam emails – and that explains the origin of all the bounces you got.

In this case you simply receive an email from the incoming server – like the usual “Mailer-Daemon” or “Postmaster” alerts – informing you that the message has been discarded.

The simplest case is when you get a bounce: for instance, when the recipient’s address is full (a soft bounce: just wait and re-send) or worst, when it’s non-existent (a hard bounce: you need to remove the account from your list). We can distinguish three main reasons why an email fails to be delivered:

It’s very important to understand the causes of an email delivery failure in order to keep all your messages able to reach their destinations.