Best posts made by ken

I see we've been mentioned here so let me know if you need any help or more info on our email security service.
Reviews for email security services from Gartner are here
https://www.gartner.com/reviews/market/secure-email-gateways
and Spiceworks here
https://community.spiceworks.com/security/reviews

Thanks Scott for the nod. The Gartner peer reviews is a tough and well moderated reviews site which asks companies on each service how they perform in different areas. https://www.gartner.com/reviews/market/secure-email-gateways .
I'd recommend picking a couple of services and contacting them for a trial. As you already have your list of requirements it shouldn't take long to narrow down who is relevant to you.