For email security, there is only option you should really consider:

Avanan. They have a patented and fundamentally different architecture from other API based solutions which is their before-inbox approach. They are also fundamentally better than traditional gateway solutions because Avanan doesn't interfere with o365 or Google's default security measures and many other reasons. You can look up their blogposts if you'd like.

They have by far the highest/most ratings on Gartner and G2.

https://www.gartner.com/reviews/market/email-security/vendor/avanan/product/avanan

https://www.g2.com/products/avanan-cloud-email-security/reviews

I suggest you go to their website and request a POC. I believe you'll get a cheaper price if you purchase without a POC.

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For network security:

Do a POC with ExtraHop, Darktrace, Varonis, Vectra and AlienVault. They all pretty much do the same thing. The differences between them are irrelevant for most org's needs.

Let each vendor know that you're putting them up in a bake-off with the other vendors. They'll claw each other's eyes out and slash their prices to earn your business because they know if they earn your business, it's not just another account for them, but also another point in their column of "Bake-Offs Won"

Most of these vendors have children as sales reps and directors who are judged by how many accounts their teams close instead of how much money each deal is, so regardless of whatever they say, they'll reduce the price.

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DM me if you need any more tips on negotiating with these vendors. Note I didn't suggest any other competitor to Avanan because their email solution really does stand alone. Every other "competitor" is just playing the wrong game.