In the US, many states have an Open Records act on the books. Typically this extends to the emails that acedemics at public universities send using their .edu addresses (among many other things). Though it varies from state to state, generally communications in and among anyone that recieves state funds in any way are considered part of the public record.

For instance, in CA the Sacremento Bee mantains a DB of all the public worker salaries, including university professor salaries, donations, grant funds, patent royalty payments, etc. It is very comprehensive and I know female acedemics that have used it to argue (suessfully) for better pay: https://www.sacbee.com/news/databases/state-pay/article22946...

In CO, there is the open records act. From what I hear, it is farily simple to obtain all emails that a professor sends out, including ones from a personal email account that happens to send out emails via a router that the state owns: https://www.sos.state.co.us/pubs/info_center/cora.html