Can masked text be recovered?

No. Masking is one-way. Keep the original file elsewhere.

Can part of an email stay?

Masking is by kind for now; combine it with hiding whole columns.

Before an outside analyst or another department gets the file, hide the columns that identify people.

Drop the CSV on "Mask personal data".
Press "Hide all personal data" or "Contacts only"; whole columns can be hidden too.
Check the preview table and save. The original stays as it is.
Save the processing report if you need a record of what was masked.

Can masked text be recovered?: No. Masking is one-way. Keep the original file elsewhere.
Can part of an email stay?: Masking is by kind for now; combine it with hiding whole columns.

The CSV is never sent anywhere; everything runs in this browser.