PS: you can use nick for in wallet chat if you want

wallet chat is still testnet only. If you can switch your nickname around, I wouldn't trust the chat.
subway
I was thinking rather than e-mail, if you send a BBP tx with an encrypted message to the public address, then the private key can decrypt the message with the gift card code. I think this is more reliable than e-mail. I tried playing around with sign message and verify message, but it wasn't exactly what I had in mind... but I guess if the message was encrypted in tx and could be decrypted automatically by the right private key holder, the process would be easy.