How to free some space on my computer by removing all emails

Hello Friends,

I need to free up some space on my Mac.

Presently, my Mac's storage shows 46 Go of Mail.

I decided to write and read all my emails online from now on, so I went into the Mail App and removed all my email accounts.

Mail app is now empty, but my Mac's storage still shows 46 Go of Mail.

How can I finally get rid of all these Go?

Thank you.