Re: Mass email function
Any shared host worth their salt will automatically, immediately and permanently suspend an account sending that many emails per hour anyway.
Any site sending that many messages needs a dedicated email server with an IP that’s registered on whitelists (costs $$$) so major providers will accept that kind of traffic. http://goodmail.com http://www.senderscorecertified.com http://www.isipp.com are examples of popular whitelist services. You also need to make sure the server has rDNS, SenderID, SPF and DomainKeys.
With some additional code and the use of cron, Detective’s code could be made to send only a few emails per minute, and track that the same domain does not get an email again within a few minutes. That might slow down the banning a little but we’re getting into spammer territory there and I’m not making such a tool available (also phplist does all that anyway).