You've probably heard of Mailchimp. I've met Mailchimp employees and heard them speak at international conferences, and these people are exceptionally great people. I just finished having a conversation with one of their fine employees about "warming up" or "maturing" IPs for mass emailing. Mailchimp currently has over 1000 IPs that they send emails from. Many of these are aged, reputable IPs which ISPs allow thousands of emails per minute go out from. In a month, Mailchimp sends several billion emails. As Mailchimp scales the outbound emails for customers, they need to buy more IPs to send emails from. These brand new baby IPs have virtually zero reputation to ISPs, and all outbound emails would get blocked by ISPs, Gmail, Hotmail etc if they started sending mass emails from them right away. What Mailchimp has is a system to gradually increase the number of emails sent from new IPs which they warm up over a six month period. After those six months, that IP is ready to work alongside the mature IPs and send millions of emails a month. Mailchimp monitors the deliverability of the emails throughout this process to make sure that the ramp up isn't too fast. I have confirmed that they do use client email campaigns for the warm up, which I find interesting. You can read more about this process by searching for Mailchimp's blog post titled "Three billion emails." My personal quest now is to determine what that ramp up needs to look like for my own domains, in order to be able to send 5k emails per day. Can I automate the sending and replying of emails between a new domain (IP) and 2000 phone verified Gmail accounts to build that authority? I'm not sure yet. If you have more insight into doing this or would like to find out more as I test things, feel free to get in touch. Cheers fellas.