I think that you will need to put the CCADDR with the TOADDR when sending the mail:
s.sendmail(FROMADDR, TOADDR+CCADDR, msg.as_string())
You’re correctly adding the addresses to your message, but you will need the cc addresses on the envelope too.
From the docs:
Note The from_addr and to_addrs parameters are used to construct the message envelope used by the transport agents.