Have you ever heard of the services Glassdoor and Fishbowl? They are services where you can "review" and "rate" your employer.
In general not a bad idea. However they require you to sign up with a valid _work email_! Crazy...
I have used Glassdoor on multiple occasions, writing reviews of my employers over the years, and I was never asked to use a work email.
To be fair it ensures quality (in terms of bonafide employee reviews) in their dataset, but it does limit its size. And also presumably skews it positive (no harm in the in-anonymity if you have only good things to say).
Can't review your past employers anymore...
The company can also pay to delete your reviews, if you didn't know this already. Glassdoor will say they won't, but, cui bono, they make their money from companies.