Blind, but I can't imagine why anyone would trust a site that requires you to register with your work email.
so yea, emails are not a trusworthy source of anything, but filtering singups based on addresses is very common.
Blind also targets having communities for people inside companies to talk, and facilitating discussion. Glassdoor is mainly about reviewing companies.
A site that requires your company email before you can post a negative review sounds like a honeypot.
I imagine HR would absolutely love to take that down.
So have up to a year after you leave the company I believe.