tl;dr: Email lists with 500+ people must be moderated and have a manager moderate them. (It's unclear if manager means 'manages employees' or 'manages email list'.) This seems pretty draconian to me, if it's true.
Not really. Big email lists like that generate tons of spam. What Amazon is doing is presumably to block unionization efforts, but, frankly, what's surprising is that they didn't have a control like this in place already. I work for a much smaller company than Amazon (without a chance of a union ever forming) and we don't let just anyone blast out emails to hundreds of people. We used to and it drove everyone nuts. People were selling their event tickets, giving traffic updates, offering up pets for adoption, etc. It's ridiculous. We had one list that was generating 100+ emails a day that were irrelevant to most of the people on the list. Every sizable list has an "owner" who controls access to send to the list. We have other channels like an area on the intranet where people can post these broadcast kinds of messages so it won't clog up people's inboxes. I thought most large companies did this.