E-mails when a form is submitted have stopped working

Hi there,

Since updating to Ninja forms 3.0.5, the confirmation emails that are normally sent to a client and admin when they submit my form have stopped working. I want to install an earlier version of Ninja Forms as I know this works. If I uninstall the current version or deactivate it, and then instal the earlier version, will I lose all my form data? Or is there a better solution.

Thanks in advance

Curtis