[Vipergrün]

Email servers typically hold the email until deleted. If you delete the message on your personal device, in most cases it will also be deleted from the server. Then, on top of that, the storage/drive of the email server could be "wiped, and not with a rag", to make sure deleted emails cannot be un-deleted. Deleting files really means nothing. Wiping your phone before trading it in really does nothing. Data can be recovered unless steps are taken to make sure it cannot.