Mailing cash is probably less private. Your mail is postmarked, and can be tracked. The serial numbers on the bills can be tracked too. Not to mention the envelope itself, fingerprints, possible DNA in the saliva when you licked it to seal it, your handwriting or printing to address it, how unique the stamp is...
Only if all that information is collected and stored. Digital finance systems tend to track every transaction and keep a record of them (because of legal requirements among other reasons). With cash in an envelope a government can't check all the info you suggested a year after the payment has happened, perhaps not even after a few days.
Mailing cash is probably less private. Your mail is postmarked, and can be tracked. The serial numbers on the bills can be tracked too. Not to mention the envelope itself, fingerprints, possible DNA in the saliva when you licked it to seal it, your handwriting or printing to address it, how unique the stamp is...
Only if all that information is collected and stored. Digital finance systems tend to track every transaction and keep a record of them (because of legal requirements among other reasons). With cash in an envelope a government can't check all the info you suggested a year after the payment has happened, perhaps not even after a few days.