Thanks for the feedback and for promising to bring up with the team. I recommend getting your coding team to actually use the interface on mobile to send their emails for a day (or even an hour). The editor would improve very quickly...
We don't need a 4 line toolbar full of options we'll likely never use on mobile, and we don't need to have the send from/to/subject visible and locked on screen the whole time we edit a message - the whole page should be able to scroll like most other systems. That example phone has a 2960x1440 resolution, but gets less than one line of actual text editor.
(It was not apparent that a minus button would minimize the toolbar: It looks like every other tool item, I would expect that would do a horizontal rule). On mobile that toolbar should all be hidden away under a tiny dropdown.
Have a look at Outlook.com or other competitive systems, which do work well on mobile for comparison.
In the meantime, we've already rolled back to SmarterMail v15 due to user pressure.