To minimize your data cost, you should set the email sync to Manual. To do this, perform the following steps:

  1. Go to Home screen.
  2. Select Account.
  3. Select mailbox (email provider).
  4. Select Update Inbox (or Schedule sync > Update Inbox)
  5. Change to update inbox Manually.

To disable background sync select Settings > Background apps > MailNo Updates or Wi-Fi only.

Note:  To minimize the data cost, you can also use the wireless network (Wi-Fi) to retrieve emails whenever possible.