The subject will be something like 'Worm Alert!', and this is what the email looks like when you get it:
Dear Customer,
Our robot has detected an abnormal activity from your IP adress
on sending e-mails. Probably it is connected with the last epidemic
of a worm which does not have official patches at the moment.
We recommend you to install this patchto remove worm files
and stop email sending, otherwise your account will be blocked.
Support Team