We Waste About 3 – 9 Hours a Year Because the Email Send Button is at the Top (nextgenui.com)

That is why designers are so important when creating a new app. And that is why you need to test your app before sending it to public.

Most of my emails are for customer support. If experience has taught me anything, it's best to keep them concise, so clicking the top button is more convenient for my usage. GMail gets it right not because there are two send buttons - one at the bottom and one at the top.