It is important to point out the several unusual things that went right in this story: 1. Your decision makers recognized that the important number to pursue i

It is important to point out the several unusual things that went right in this story: 1. Your decision makers recognized that the important number to pursue is "engaged users", not "number of emails in the list". 2. You have a large enough subscriber base so that Gmail/Outlook realize you're a good player. This wouldn't happen if you only sent a few thousand mails per week. 3. You have the technical expertise to properly maintain the list and the surrounding (unsubscribe, etc.) infrastructure. Usually the budget is allocated to _create_ the list/service and then assumed that it will continue working forever with 0 investment. IF you can get these things right too you'll (eventually) have a similar experience. If you fail on any of them... you're screwed like everyone else is saying. Of course, having to send large volumes of email to ensure that "the big guys" treat you fairly is why many people running small/personal email servers complains about them.