Re: Samsung Galaxy s6 - how do I select ALL emails for deletion?
Welcome to Android Central! There often isn't an option for this, as it is potentially dangerous--it might be better not to have a Delete All selection than to have one and accidentally delete all of your emails, including very important ones!
You're talking about the stock Email app, right? What are you using as an email provider? If it uses an IMAP server, then the emails shouldn't be taking up physical space on your phone's storage, since they're essentially read from the IMAP server. If it's a POP3 server, then the phone actually downloads the emails to your phone, which can take up storage. If you're worried about your storage space and if your email provider has an IMAP server, then use that instead.