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.

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

"Because they are sales people, not technical people, and they are only paid to sell you something. So if you ask their technical advice, this is the best that they can do...."
The idea that a vendor company only consists of Sales people is ridiculous. Does Red Hat, Microsoft and a host of other vendors, simply consist of sales people?

It's definitely in vogue in a retro, don't you remember when you were a kid in the 80's and used to copy games from a book into your Atari,(I hope my kids have better things to do) kind of way. Paul Bunn was one of the authors I remember.
Probably not in vogue in a , I'm doing classes in BASIC now, thinking it's relevant, kind of way.

So do you get advice from "consultants" who are partnering with vendors? I feel attracted to this conversation like a suicidal moth to a flame.

Wow, that's definitely surprising. Morocco is the second largest "Direct sight Ocean Neighbour" to the US. The amount of South America below New Zealand, considering how cold the very south of NZ is. Great visual.

I'd only buy telecoms from a telecoms company. Best of luck to them with their all-encompassing we'll sell you anything approach but I fear it may not work to well for the customer when they need help. Call me skeptical.

Hi, Ken from The Email Laundry. Katie told me about you so I had to take a look. If you have any bizarre email troubles I'm always worth a shout. If I don't know the answer there's definitely a few people within a shoe throw who can help.

@steve Great to know guys. Best of luck with it Steve. It seems to be a very smooth running service. Does it have a mobile element?

@scottalanmiller I think the cloning rumours must be true so. Who set up Mango Lassi? Someone just told me about it in London yesterday.

@scottalanmiller If it's done, I haven't seen it. So are you not on SW any more?

@scottalanmiller Sorry Scott. It was the keg stand. I had just logged in, hadn't got very far down the thread. I didn't realise the vast array of useful information I could encounter.

@scottalanmiller At last I found something educational on one of these sites. I can't believe I've never heard of that before.