Strange exchange mail behaviour on Cyanogen OS

I have a Wileyfox Spark X running Cyanogen OS 13.0 and use the Gmail app and the stock email app for personal and work mails. The stock e-mail runs into problems when I reply to an e-mail thread. Instead of sending the mail, it goes to an Outbox, its status changes to 'Sending...' for all eternity and there is no way to make it re-try. That makes it practically unreachable - the only thing I can do from here is deleting it. New messages such as ones with only 'test' in them are sent, but not usually straight away - often only after I have gone into settings - incoming server and made it re-authenticate. All in all the stock email app seems to work in a completely other way than I am used to or not at all. Does anyone know the cause of this strange behaviour and how to change it? Previously on CM12 I was running TypeApp which was brilliant with Outlook Exchange (which seems to be bad system for phones in the 1st place). It seems wrong though to have the stock app there doing nothing...