There are rate limits in place to prevent email spamming. The system stops creating new accounts for a domain where the percentage of unconfirmed accounts is to

There are rate limits in place to prevent email spamming. The system stops creating new accounts for a domain where the percentage of unconfirmed accounts is too high. There is also rate limiting on client IP, disallowing client IPs to create lots of unconfirmed accounts. I am also planning to, but haven't got around to it yet, add exponential backoff to email sendouts, so that an increase in the sendout rate causes sendouts to be slower and slower (until manual intervention to increase limits). So, in short: yes, the system could be used for email spamming, but not very effectively. There are better options if all you want to do is spam people.