[SC-Help] Loads of spam showing "Delviery Status Notification", "Failure Notice" etc.

[rowan]

I've recently started receiving loads of spam messages which purport to
be delivery failure messages. They are always addressed to a
non-existent user at my domain, e.g. ojvnyo@, ejrzx@, rrl@ etc. They
can have a variety of failure messages, and purport to tell me that a
message that I sent to an address that I have never sent to in my life
could not be delivered. The message sometimes contains a load of Base64
code, presumably some kind of malware, or a scanned page of text.
Sometimes there's no obvious payload.

Where are these messages coming from? Why have they suddenly started
(or at least, suddenly started finding me)? Why are they getting
through my ISP's spam filter (which is normally very good)? What can I
do to get rid of them?

Many thanks for you help - Rowan