THANKS! for clearing that up. I apologize for the misinformation and can only claim gross ignorance seasoned with stupidity; I'm not now even sure where I got that idea (and it is bugging me!)
Please understand that I was specifically told via a support email that email quotas only impacted a given user when I had a script run amok a few years ago. And, in that instance, it was only a single of my users whose mail sending privileges were curtailed for a few hours until I whipped an errant form mailer into submission; the other users on my account were not impacted. Hence, to prevent all my sites from losing their ability to send mail should a single site get exploited, I began establishing new sites as separate users.
This, the email quota, actually, was my main reason for advising this, and I agree that it would be counter-productive to the whole program to use multiple user on the same machine to obfuscate CPU/Memory usage - the machine suffers from over use either way.
I'm also in complete agreement that there are better ways to use one's time than managing multiple users in your account, though sometimes it really can't be avoided if you need to share access to a given domain, due to security concerns.
Hearing now, that all domains hosted under a given account, irrespective of the user, are combined when measuring CPU/Mem usage makes sense, but I am now again concerned about the management of email quotas. I also noticed this morning a recent edit to the DH wiki indicating this is also true with email quotas, and that is really discouraging.
It virtually guarantees that if you host more than a couple of domains that have interactive features (sign-up confirmations, lost password retrieval, new post or message notifications, etc.) you will easily run afoul of the email quota. A a few popular threads or two on a forum where several users wish to be notified of new postings could burn through this quota very quickly; God help you if a digg or /. reference sends a lot users who want to register to your site; when you most need the system to work it is likely to break and prevent them from receiving their "Welcome email" (which in some cases may contain their account information or an activation link).
The same type of traffic could be responsible for numerous "contact form" submissions (many of which are set up to email the site owner and cc the sender). It also pretty much precludes the use of any "tell a friend" interactivity; multiple sites with any traffic would combine to quickly exceed the by account quota. I'm afraid that even a single busy site would not be able to use these email features, and these are all commonly expected features of an interactive site.
If all users/domain etc on an account have their email usage accumulated into the single quota total....hosting multiple site with any degree of user interactivity at all would be become virtually impractical.
I agree with you on CPU/Mem usage, and I guess I must have just made a disconnect somewhere with that information, and am actually glad to have that clarified...I apologize profusely for the misinformation.
That said, can you please confirm/deny or further clarify the way the email quota numbers are accumulated? That is critically important to me, and my clients, and I don't want to remain confused about this or set my clients up for serious dissatisfaction if this jumps up and bites them!