Re: I lost all my emails on my IPhone 6
Welcome to iMore! Go to Settings > Mail, Contacts, Calendars, select your email account, and then tap on Delete Account. Once that's completed, tap on Add Account and follow the process to add the account back.
If that doesn't work it's probably because 1) your email settings with your provider are set to not sync email with your phone or 2) you have your email account set up as a POP3 account on your iPad and it's downloading the emails to the device and removing them from your email servers.