Apple's iOS Mail app enables you to customize how email messages are delivered to your device. You can use the Push method (default setting), where the mail server will automatically push new messages your iPhone or iPad; the Fetch method, where the Mail app will poll the mail server at regular intervals for new messages; or the Manual method, where emails are checked only when you open the Mail app.
This guide will run you through the steps required to set up your email preferences in the Mail app.
You can configure your mail settings for each of your individual email accounts by going into Settings > Mail, Contacts, Calendars.
Tap on Fetch New Data, select the desired email account and toggle the Push switch Off. In doing so, you will automatically enable the Fetch mode.
Now it's time to set up the email check frequency for the selected email account. You can configure iOS to automatically check for new emails at regular intervals (Every 15 Minutes, Every 30 Minutes, Hourly...) or use the Manual mode.
N.B. The Manual mode is preferred in situations where battery usage is paramount.