A radio sent a letter in the mail

I think there may be a bit of a misunderstanding here!

Radios are electronic devices that transmit and receive audio signals, but they can't actually send letters in the mail. Letters are physical pieces of paper with written or printed messages, and they require a physical entity, like a person or a machine, to send them through the mail.

So, it's not possible for a radio to send a letter in the mail. Perhaps you're thinking of a different scenario or a creative idea? I'd be happy to help you explore it!