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This article is a step-by-step guide on how to get to a scale of 100k emails per day with a 95% inbox rate. Set up DKIM, SPF, and DMARC are ways to authenticate your mail server and to prove to ISPs, mail services and other receiving mail servers that senders are truly authorized to send an email. The best and cheapest tool for scheduling is GMass. For 150 users, you’ll pay $1591 / month for 150 users.