Messaging with Rails and Mailboxer

I need some way a user can send the same message to multiple users but keep the conversations separated.
I guess this may sound weird and it misses the all idea of conversations.

I was thinking I could make this the default behavior and add a checkbox on new message view to set the message to be a private conversation (splitting it) or grouped.

Does it make sense? Is it possible or am I thinking it the wrong way and should build something from scratch?