Saving incoming msg object to reply later (Serialization Error)

I guess I am still confused about how I should approach saving an incoming email message so I can reply at a later time to the original thread. Is the Message object only accessible within the
functions decorated with @anvil.email.handle_message() upon incoming?

Or do I not even need the message object to reply to the thread? It seems that anvil.email.sending an email w/ same from and subject would send them an email in a new thread.