In the vast majority of email clients I've seen (Outlook, but also Web mails like outlook.com or GMail), the "Send" button is always next to danger zone where the user often clicks. The worst example being Outlook, showing a UI like this one for ages:
It's pretty obvious, even to a UX neophyte like me, that the "Send" button is kind of dangerous and should be isolated in the UI, so we cannot click it by mistake. Who has never sent an email by accident because of the position of this button?
Also, when you compose your message, and when you check it before sending, it would make sense to proceed from left to right (or right to left if you're in a RtL locale): you review the headers, and then you click Send. Not the other way arround! So, this kind of UI would be much more convenient:
Or even with a "Send" button below the message body area, as do e.g. with Web forms.
This question adresses the "how to workaround this problem", but I'm asking about the reason leading almost all major email clients to keep the "Send" button close to the other buttons, or without a clear visual distinction.
For instance, this answer explains pretty well what could/should be done… but not why on earth didn't Microsoft (to name a few) did not implement a proper solution in decades.
While the whole UI is constantly redesigned in these email clients for a "better
world user experience", the "Send" button is always kept on the left, and always easily clickable by mistake. Is there any actual reason?