This is a suggestion as it will make ERP more user friendly for the CRM users or email integration users. Zoho has a very good CRM functionalities which I think if incorporated will make it very user friendly like the one shared above i.e. Collapsible communication / email / comments.
If needed I can share the videos as well with your team.
I think your suggest would be very useful. The email features have been improving steadily, but there are still areas that ERPNext lag behind such as what you have pointed out. the problem is resource really. Frappe are very busy with many other things in ERPNext and although probably not a ton of work, there are so many other good Feature Request in Github that it may take a while before this could be realised. Email can be used throughout the whole application so its important to my mind that underpinning features can be improved as well as separate sections and new Domains.
If i were you, I would create a GitHub issue (Feature request) of this with the graphics so it can be +1’ed by any others so frappe and the community understand if this is an importance or priority to them.
If this is particularly useful to you, please consider creating a Bounty too, so a number of us can club togther to get this developed. I would be happy to add to the pot if you make this a bounty