iPhone 6S IOS - Freeing up space in mail is NOT working

Do you post a lot to social media apps? If you go to...

Settings / General / Storage & iCloud Usage

It'll show you which of your apps are sucking up the most space. You can delete and re-download apps that you use frequently. Uploading images to apps such as Twitter, Instagram, and Facebook are the biggest hogs of "free" space. Also, you can purge the search history of whatever browser app you are using.  And, don't forget, iPhone's native apps also eat space too such as iBooks, iUniversity, Podcasts, etc.

I deleted all email accounts  <-- Now shut your phone OFF. Hold the top button down, pause, swipe Power Off. Wait 1 minute, and start it back up.

Now check storage again. Does it change?  

(I have an iPhone SE == 6s)

Mail doesn't use much space so focus on stuff like messages, music and photos

I deleted ALL email accounts. and my manage Storage shows that I have 71GB in mail storage and 10.2 GB in Photos and Camera.

I did shut off my iPhone and turn it back on. No change.
I even did the IOS upgrade to 9.3.5

That's weird. I've never seen mail take up more than a couple hundred megabytes.  Are you using POP accounts by chance?

Also did you turn mail off in settings or delete the account fully? You'll need to delete them all the way.

My personal email is POP -- which I deleted
My work email is IMAP - which I also deleted.
I also had a HOTMAIL account configured in my iPhone mail system --which I also deleted.
No change in free space quantity.

Hi John:
All I need to do is migrate the Reminder file on my iPhone, my many videos and photos,  my "favorited" articles and my "notes"

Thanks everyone for the help. Turns out, I'm screwed.
None of the posted solutions work so I have to RESET my iPHone completely.

That was what I had thought might happen. Thank you for the update and I hope the reset provides a good working base for you.

I have never reset my iphone.

There's another memory hog that you may not be aware of. If you currently don't automatically send diagnostics and statistics to Apple, you should toggle that on. Hard reboot the phone (e.g., power it off, wait a few secs,turn it on again). Those app crash error reports just keep on piling up.

I have reset phones on one or two occasions and I power it off each and every night.

Do the erase and restore first. I bet that will clear up the space and cause the least disruption in your phone use.