OT - my domain must have become a spammer's source

[Craig White]

I have long had a catchall box for my domain without too much issue -
spamassassin has handled the load.

Apparently - starting at some point today, I am getting several hundred
rejects an hour with apparently random_name at azapple.com as the sender
and thus the bounce backs/rejects are coming to me. 

I can filter them with sieve but I am wondering if there's a way to know
how/where these things are originating from and if there's likely any
reprecussions from this mess.

Craig