After a few mishaps where some folk sent an email reply instead of a comment, my team (understandably) avoids commenting on email threads like the plague.
This is an issue for me.
I have support experience in a company with multi-award-winning customer support, and I know that comments/documentation is everything (weird flex).
At the very minimum, it'd be helpful to have a configurable (or long enough) "delay before sending" option so that we can 'unsend' the email or rush to a colleague to tell them to unsend it before it can cause us some embarrassment.
I think an approach that's somewhere in the direction of the example in the attached image would be better for UX (adds actions), and the concept in the image isn't very obtrusive. But approach it how you'd like.
Note: I've clearly made no attempt to make it pretty. It was done in ms paint.
The vertical ellipsis can contain "Convert Reply to Comment" and even "Send Now", leaving only "Unsend" in the open.
Thanks for your time.