Alright, thanks for the info. My service hasn't launched yet, but once it does launch I will most likely exceed the 500 domains per 3 hours IP address rate limit for the first week. I definitely won't need a limit exemption after that, but I still would like my launch to go smoothly. @jsha Is there a specific email address I should contact prior to launching my service to ask for a temporary one-week rate limit increase? I expect at least ~1000-2000 domains per 3 hours during the first launch week, though it is hard to definitively gauge interest with the data I've collected so far. It's very likely that I will exceed the 500, and pretty much guaranteed to happen for the first launch day.
(Btw, this isn't urgent. I won't be launching for about 4 months)