Just had my old phone put back to factory settings, when I tried to open it to check my emails had gone, it said Connect to WiFi /Welcome/Start. Does this mean all is ok, and no one else could see my emails when they put in a SIM card? Sorry not technical !!
It should be exactly as it was when it was turned on for the very first time and it would not be easy to recover any of your emails, details or other data.
You can safely sell it or dispose of it if that is your intention.
your phone just needs to re establish connections to things that you log into. Email is just a web site that you log into. What email program do you use?
Your client can opt to delete from the server after downloading successfully, so it is possible the e-mails won't be automatically available, depending on how thorough the 'back to factory settings' is. Less likely for a mobile though. In my case it's the PC that deletes from the server after downloading the e-mail.