this post/feature-request is a side effect of another missing feature:
possibility to edit sent messages
and maybe also a better “full screen” editor to preview/review long messages better before sending, currently with only like 3-4 lines of text in the composer it is hard to read long emails/messages before sending
about editing sent messages there are already these features requests:
with the ability to edit messages and/or better full screen composer to read the message before sending, the issue would be solved without needing less user-friendly approaches like “send” and “really send” options.