[aminok]

You can have a micropayment channel between the user and their email provider, and between email providers.

When User A wants to send an email to User B, he sends a micropayment through one of these channels to his email provider. His email provider in turn sends a micropayment to User B's email provider. User B's email provider sends a micropayment to User B.

So in this way, value can be transferred without any on-chain BTC transactions, zero fees, and instantly.