Need to turn off spellcheck and autocorrect.
I can't find any way of disabling these features; they simply get in the way of emails, especially informal ones (where one may indulge in non-standard coinings).
I found an entry here concerning opt-out of autocorrect, which was marked Completed, but doesn't seem to be available anywhere. The down arrow hides the bar, but it comes straight back. This "feature" generally acts like a bug.
I note this was recently added to the OneNote app, which I can now use far more comfortably, but it lingers in Outlook. Deeply uncivilised. Hoping that it will be implemented soon.
Angel Robert Lynas commented
Gosh darn it. Apologies, it's in the General iOS settings. Newbie alert, I've been a Windows user for ever. Your very good health!