With many of the big email providers they don't block on the basis of the number of messages per hour or minute or second, but by the concurrent connections. It’s a juggling act here to try and keep our addresses clean to make sure everything gets through. To answer your question though, no we don't send out to everyone at the same time. Although, I sure would like to send them out all at once. :) Yes, Server side whitelisting goes either by domain or more often by IP. Domain and email level whitelisting is still something that needs to happen on the user end though as most places have implemented user defined whitelists. These are typically not done by IP.
