Any sane corporate security? You can setup gmail account in 5 mins and start phishing people in corporate env. That is why receiving emails from generic domains is no go. I also had actual requirement where we did not allow people to register with gmail account, only non generic domain emails allowed. So that you use your company email for B2B product.

How big is your list of 'generic domains'? There are email providers that give you hundreds of domains to use, and only take 5 minutes to register.

Any? So Gmail users can't email any sane corporation?

Extraordinary claims require extraordinary evidence. Please provide just a single reference to this claim.