tl;dr: Looking for the best affordable method to send an email to a large unsoliciated email list. Also looking for recommendations on effective methods of creating a double opt-in, or opt-in, mailing list targeted at business owners? I just started a mobile application development company and I'm trying to get the word out to realtors in different states. To do this, I have scraped a few sites and I have obtained ~40k emails of currently active realtors. I would like to send an email to each of these individuals, only one time, to find out if they are interested, if I don't receive a response then I will not reply to them again. I have done this on MailChimp a few times already, but services like that are quick to ban you. What is the best way to send emails to these addresses while offering an opt-out link and a short message at the end stating that they will never receive another email from me again if they are not interested? After a day of research I've found numerous responses saying a VPS with IP Rotation works great, but with IPv4 addresses exhausting is this still the best method? Are there any cheaper alternatives?