A lot of provides on shared servers limit how many numbers of emails can be sent per hour.
I had to send thousands of emails a day for a client (nationally known name brand), totally legit and was a sign up (opt out) to get a newsletter.
I used swiftmailer and had to get a dedicated server (that would get shut down if it was spam).
if you have a client like AARP and have a newsletter, you can't send spam when you have thousands of subscribers.
When someone asks to send thousands of emails people automatically think spam but that is not always the case.
help people and not be negative.