Report to show incidents with replies

Content

I am looking to get a report that shows all incidents that have a reply from the sender.

I thought to use all incidents that have the 'Updated' status, but this is also being used by agents internally, so am unable to use this.

I thought to use the transactions table, but there doesn't seem to be a transaction type that is sender sent response to email.

So, does anyone know of a report that exists or that can give guidance on how to create a report that shows me all incidents that have a response from the original sender (that are not resolved!)?