Interestingly, I had a kind of DOS attack on my email account when someone gained access to a credit card account of mine and used it to send money to themselves - I got inundated with hundreds of random emails per second when they were sending money to themselves, so as to make it hard for me to get the notifications and do something about it.

Fortunately, the pattern of emails wasn't very sophisticated and I had made a rule to filter them out within a few minutes and had the account closed within 5 minutes, but I can see how this would be a pretty effective tactic against less computer literate targets.