Why are all my old emails downloading to my phone?

[iMore Question]

This is the third time this has happened! The 2 previous times it was when
I got a new iPhone (iPhone 6). I still have the same iPhone 6 and have not done the last 2 updates. I have 2 emails accounts and they have each downloaded 10,000 old emails each. If I delete 1,000 I get 1,000 more. Now on top of that my battery dying quickly! How do I stop this and how do I delete all of them with out doing it one at a time?

 

[Just_Me_D]

Go to Settings - Mail, Contacts, Calendars, - (email account), and then edit the time set next to "Mail Days to Sync", if available.