It's really none of my business, but whenever I read questions like this, alarm bells go off, as all of it sounds just too much like spammers at work. How else would "adding 2 million email addresses per day" be a legitimate endeavour? (Apologies if I'm getting something wrong here.)
While a self-hosted platform uses the individual server's IP address and reputation drops and ESP blocking will not affect other MailWizz clients directly, I'd hate to see MailWizz becoming the spammer community's weapon of choice. It would make me feel very uneasy. It would impact the MailWizz reputation and our ability to attract genuine, reputable customers to sign up with a MailWizz re-seller.
Not sure if there's anything we here or the MW team can do about this. It just doesn't sit well with me I have to admit.