[EGreg]

What messages can’t be sent as sealed sender?

I arrange to tell Alice in an encrypted chat that I will be doing a drop on X url after Y time and to watch it.

Alice comes picks up the drop. Done.

PS: This is another great use for cryptocurrency. When you don’t want to use account-based charging, then you allow anyone to prepay for the resources with crypto.

[ikawe]

For example, before you have Alice’s sealed sender authorization credential, you cannot send Alice Sealed Sender.

This happens upon initial contact and after Alice revokes her credential (which can happens if she blocks someone).