Let’s be realistic, that isn’t an equivalent alternative
Sending mail is pseudo-anonymous at best. It’s exceptionally slow. Most importantly, it’s insecure to the point where most postal services explicitly recommend against mailing cash
Because there is a lot of evidence tied to mailing a letter
DNA
Fingerprints
Time and location the letter was mailed from
Camera footage of you mailing the letter
The letter itself can generally be traced back to where it was manufactured
Address handwriting/stamp/sticker
Even if you scrub anything personally identifying yourself, it still leaves a fairly unique fingerprint. A sufficiently motivated investigator would be able to identify another similar payment without inspecting the actual contents of the letter. Hence pseudo-anonymous
You do know that you can pay for mullvad in cash?
You can send cash in an envelope to them with your mullvad ID and they will credit your account.
Can I go to their HQ, slip them a tenner with my ID on a piece of paper under the door?
Yes
Let’s be realistic, that isn’t an equivalent alternative
Sending mail is pseudo-anonymous at best. It’s exceptionally slow. Most importantly, it’s insecure to the point where most postal services explicitly recommend against mailing cash
How is it not anonymous?
Because there is a lot of evidence tied to mailing a letter
DNA
Fingerprints
Time and location the letter was mailed from
Camera footage of you mailing the letter
The letter itself can generally be traced back to where it was manufactured
Address handwriting/stamp/sticker
Even if you scrub anything personally identifying yourself, it still leaves a fairly unique fingerprint. A sufficiently motivated investigator would be able to identify another similar payment without inspecting the actual contents of the letter. Hence pseudo-anonymous