Comparing email providers based on the email features they offer arises from a fundamental misconception. In the context of a well-defined email protocol, providers should not have the capability to modify the protocol itself or introduce distinctive email features.
Consider a parallel scenario: when was the last time you heard of someone evaluating web hosting services based on their implementation of custom HTTP features? Such an evaluation doesn't hold water because the HTTP protocol is meticulously defined and serves as a foundational component. Any supplementary features that a web host might introduce would have limited applicability since the protocol's standards are firmly established, and HTTP clients (browsers) do not accommodate personalized alterations. Email should adhere to a similar principle.
Email providers should be incapable of altering the fundamental email flow or having insight into it, even if end users desire such modifications, as their primary role should revolve around storing and forwarding messages. The only scenario in which such modifications should be possible is when the email client itself is the service provided. Webmail services exemplify this scenario.
Any additional email features should be integrated into the email client rather than forming part of the provider's service offering.