I wrote about that just now: there are rate limits in place to prevent it. You'd have to go to quite a bit of trouble to be able to use the system for any kind

I wrote about that just now: there are rate limits in place to prevent it. You'd have to go to quite a bit of trouble to be able to use the system for any kind of effective spamming, coming from different unique client IPs and only send a few emails from each of them, and not send too many emails to the same domains (e.g. spamming gmail.com would be impossible).