Mailchimp is pricey, but with the promise of helping you achieve deliverability and support you when things go wrong.
which is exactly why we were totally dismayed that as we found out a major provider was rejecting our mails (not by mailchimp reporting it, but by an external tool), Mailchimp eschewed all responsibility nor tried to provide significant help. Everything about its conduct yelled "it's your problem'. Even data that was needed to properly diagnose the problem was not shared with us.
Needless to say, we will never use any RSG product again. yep, that bad.