As @Randy Calvert mentioned, AWS SES is one of the lightest and cheapest transactional email services available. I would highly suggest it with the volume of email you are sending. They also have one of the highest reputations which only helps your email deliverability. Our instructions are very detailed and should be easy to set up. If you have any questions, just reach out and we’ll get it solved for you. It’s a set it, and forget it type of solution.