That makes sense. I'm leaning towards segmenting my plans in a hybrid way that restricts advanced features to higher plans, but charges a fixed $X/unit for all

That makes sense. I'm leaning towards segmenting my plans in a hybrid way that restricts advanced features to higher plans, but charges a fixed $X/unit for all tiers. That way you can pick a plan based on the features you need, while still being able to easily calculate whether $X/unit makes sense for your margin. Like you said, if you upgrade a plan, you rightfully expect more features. The reason we can't do a flat $X/unit alone is because we are not an email API, but rather we see ourselves as a booster-pack for email APIs. We don't sell emails, we sell email delivery optimization tools. Yet still, the volume of emails that flow through our infrastructure really matters. Plus, some of our features, like an Elasticsearch integration, are really expensive for us to support, so it makes sense that we should restrict those features to higher tier customers. Thanks again, super helpful comments.