I've struggled with that, having been in the same position - I was a "VP" at a six-person startup over ten years ago. Of course, I didn't anything remotely VP-ish there - I was programming computers, same as I've ever done. But, that was my title. So... do I write that on my resume and be honest about my title or write a title that's honest about what I was actually doing?
IMO it's always fine to be creative when listing a past job title, PROVIDED you are trying to provide more accurate information and not deceive. I've had titles that do not at all accurately reflect my day to day, so I list them as something more topical. However I will never portray myself as having more authority nor more day-to-day experience than my title would have otherwise conveyed.
Yes, I never use my official title in the company emails. There were some funny moments in the past when some people thought someone reporting to me was my boss, but it was always funny. These days people in my team have more impressive titles than me, I am totally fine with that.