Responsive/dynamic height repeating group

I have a 2 column page layout with a list of messages in a repeating group on the left and the message content on the right, essentially like most email clients. (See attached image.)

How can I make the message list (repeating group) height responsive with vertical scrolling.

Bump! Anyone?

YouTube has many great videos on this subject!

It’s always easier to see an example vs reading an explanation.