When it comes right down to it, the words you write in an email and send through your company server are not yours- they are the property of the company for which you work.
So if they keep them for 100 years, as required by law, that’s not a big deal, right? After all, it’s their property, and they can choose to use it however they desire.
Right?
If you don’t think so, I guess the place to start is right here.