Invoices, thousands of em
We have been getting a steady stream of them for months, usually to spurious email accounts that don't exist so end up in webmaster for me to delete.
They are usually glaringly obvious as spam ( though not to our spam filters it would seem :( ) and merely lead to premature wear on my delete key.
I can see why some minion operating on auto-pilot may be daft enough to pay one, though even they should really know better.
From all our experience it takes a hell of a lot more than an invoice email to get customers to pay!
Damn spammers, grrr