Hey there Studiovic and sorry to hear about the disappearing emails. We have asked our IT Team in the past about deleted emails and I'm afraid if it's been deleted from the user end, we're not able to retrieve the emails for you and I'm sorry about this.
Can you confirm what device(s) you're using and the third party email app? Can you view your emails via webmail or is it just the third party email apps? Also have you tried uninstalling the email account from the App and then re-adding it back on, do the emails load up?