When it comes to ESP for affiliate marketing, you need a platform that allows high-volume sending, good deliverability, and flexibility with compliance. Many mainstream ESPs like Mailchimp and Constant Contact have strict policies against affiliate marketing, especially in these niches. Instead, I’d recommend looking into self-hosted solutions like https://www.mailwizz.com/ or Interspire, which give you more control over your campaigns.
For SMTP providers, https://aws.amazon.com/ses/ and https://postmarkapp.com/ can work well, but if you need something more flexible, services like PowerMTA or https://www.smtp.com/ are often used by affiliate marketers. I also think warming up your domain properly and using tools like https://www.neverbounce.com/ to clean your lists can significantly improve deliverability. And if you’re going for bulk sending, setting up your own mail server with https://github.com/postalserver/postal is another option.