custom forms send to custom email
Suggestions
At the moment a listener would be the way to do it:
Docs: "Events and Listeners"
https://www.jamroom.net/the-jamroom-network/documentation/module-developer-guide/1011/events-and-listeners
The jrUser_notify() function is the one that does all the sending and checking of users preference of how they want to be notified and it has an event trigger in it 'notify_user'.
OR if you're only interested in emails, then there is the event 'email_addresses' in the jrCore_send_email() function.
You could use your listener to add any address you wanted into there.