As pert of April ' 20 Wave 1 release , Microsoft has brough in a new feature to compose email in a pop-up, non-blocking window, with the ability to write an email with context of the current record, navigate between records, and have multiple active draft emails open simultaneously.

https://docs.microsoft.com/en-us/dynamics365-release-plan/2020wave1/dynamics365-customer-service/familiar-modern-email-experience-agents

Idea : Extend this Feature to replying and forwarding of emails.