I have installed the newest version of MyBB just to test it out on my HostGator account. However, I do have a question about the mass email feature: HostGator only allows people to send out 500 emails per hour. So, is there any way to throttle emails with MyBB? For example if I have 2000 members and want to mass email all of them, how can I do that without violating HostGator's TOS?
I don't think there's a way.
Yes, there is, that's what the per page setting is for.
The Mass Mail is a task, and tasks are triggered every time someone visits the forum. There's code in the footer that checks for tasks and executes them if necessary. If the Mass Mail task is set to run every 15 minutes, it'll run after 15 minutes of the previous run once someone triggers it, if that makes sense. So, if you can only send 500 per hour, and if it's set to run every 15 minutes, I'd set it to send no more than 100 emails each time, leaving 100 free for that hour to cater for other emails that the board send, notifications etc. Depending on how quickly you need it sent out, it may be best to set it to something like 50 so it doesn't slow the board down as much when they get sent.