Why is Apple Mail showing as 61GB?
Mail is one of the easiest to clean up in most cases.


Verify your mail providers have all of your mail stored in the cloud.
If you are cloud based, remove each mail account one by one, then repeat the measurement of the databases.


Usually it’s attachments and indexing that take that much space, but when you delete the mail account from settings, that should clean up all the local storage.

If you have local copies of mail, you’ll have to export / back that up to be sure you don’t lose those mails before removing the account.

How much space is used once you delete all accounts or get a good backup and then delete accounts?

If you show a screen shot of how you're measuring, we might have some extra advice, like not using the system information if there are time machine local snapshots (or how to purge them) or if you just need to remove some library files or ask for a database "vacuum" process.