as i know xapo had the service, where you were able to send bitcoins via email, but i am not sure 100%, you can check it,
good luck...
Would that send to the address or to the xapo wallet?
i think both of you, sender and receiver must have xapo wallet and send bitcoins via xapo. i was using xapo several years ago, and from faucets i was receiving satoshis using email, not btc address.