To handle large Distribution Lists:
1. You could hide these lists from the Global Address Lists, but synchronize them using Syncronym, and just the PoliteMail users would have access to these lists (and be able to create their own targeted lists), using PoliteMail user/group permissions to control and send permissions to these lists.
2. Exchange/Office365 offers features to control send permissions to mail enabled security groups (distribution lists), either using the moderation features or the send as permissions in Office365.
To prevent employees from sending to or replying-all to large or protected distribution lists, here are a couple of options to consider: