Mass emails are very different category, normally mass email blasting take up the nearly the entire CPU and I/O resources of an email server leaving near zero resources for other hosting clients.   Therefore our normal advice for those who wants to mass mail is to get your own dedicated servers so that you will not cause problems for other users on the same system as you are.

Another hazard of mass emailing is that of being blocked by Spam Block Lists, you may have all opt in emails,  but it does not take a few of such optin users to forget about having opt in to your email list and send their complaints to the RBL Spam Block Lists.   Such actions might cause all users for that particular email server to be blocked by the RBL list.  Henceforth, it is not that our company are particularly strict on mass emailing, it is that the effects are too bad for others who are using their emails for normal services.

Also mass mailing has another big issue, that is ISPs and also popular Free Email services are now learning to block mass mailing through grey listing and tarpitting, these in terms greatly slow down our email servers as a result.  Therefore for the good of all, those that need frequent mass emailing, it is best to get your own dedicated servers and also get a email blasting software that can toggle the email bursts so as not to trigger the tarpitting and grey listing effects of the ISPs and other email receipients.