Settings/Apps..scroll to Email..scroll to App details in Store..below is a second line App details in Store.tap it. It will bring you to Play Store Tap Uninstall. It will ask you "If you want to uninstall updates". Select "Yes". Tap on 3 dot symbol on top right and deselect auto update
I was able to uninstall updates to Samsung Email, but problem still persists - some emails just won't download the content, even though the Inbox shows the message has been received. I should add that the account is setup as IMAP in the app.