This article about LinkDrop protocol introduces a method to send tokens without the receiver having Ethereum address, aimed at solving onboarding issue:
It looks similar to TokenScript's attestation work, which enables one to send a token to another by email address without knowing the recipient Ethereum address:
The work was part of the undergoing in the weekly TokenScript Thursday work-group meetings. Today is Thursday again, shall we talk about it this evening?
To me, it seems LinkDrops model (“Send with attestation”) requires a secure channel to delivery, but no requirement for the receiver. The attestation protocol (“send to attestation”) doesn’t care the secure channels but requires the receiver have or can get an attestation.