Instagram's API does not return the user's email address. This is a limitation in their API and not something we can work around. The only option JFBConnect has is to bring them to the login/register page and allow them to fill out their email address. Other details can still be automatically imported.
Twitter used to be this way as well, but thankfully added email as a field that could be fetched about a year ago. If Instagram ever changes their API to allow email to be imported, you can be sure we'll support it as soon as we can.
I hope that helps explain,
Alex
Instagram Registration
