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4 months ago3 years and counting here, I host my own company email and a couple of clients, 120 email accounts and only had one issue with a compromised account, limit each domain to 100 sended emails and I can catch spam emails with enough time before my vps provider notice anything
Within 24 hours, if you think about it you don’t send more than 100 emails per day and more than that is more reasonable to send it with some mass-mailing system