Can't install HTML email signatures on iOS 10
There's currently a bug in iOS 10 that doesn't allow you to shake to undo the automatic formatting changes, when you paste your HTML email signature into the Mail app's signature settings.
How it worked in iOS 7, 8 and 9
In iOS 7, 8 and 9, when you paste your HTML email signature into the Mail app's signature settings, you shake the iPhone to undo the auto-formatting changes that their software applies to the HTML. The popup message reads "Undo change attributes". You press Undo and this reverts your email signature back to how it should be.
Why it doesn't work in iOS 10
However, in iOS 10, when you paste your HTML email signature into the Mail app's signature settings, when you shake to undo the auto-formatting changes that their software applies, the popup message now reads "Undo Set Writing Direction", which does not undo the formatting changes.
What's being done to fix it?
We reported this bug direct to Apple through our iOS Developer account along with screenshots and detailed information on 18th September 2016. Until Apple fixes this bug, unfortunately there is no way to install your HTML email signatures into the Mail App on iOS 10, unless you rollback to iOS 9. If you have installed your email signature in iOS 9 and then upgrade to iOS 10, your signatures will work.
No other email apps seem to be affected, this is an issue with the Mail App only due to changes made by Apple from iOS 9 to iOS 10.
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