The iPhone, iPad, and iPod touch have an ability to click your e-mails automatically. The way this works is that your e-mail server will automatically push your e-mails to your device as soon as they are ready. This is known as push e-mails.
The challenge with push e-mails is that if you get a lot of e-mails during the day your phone is constantly beeping or vibrating at you to tell you that another e-mail has been received. Also, if you are out and about you could be using up a lot of battery or your phone data getting these e-mails when you do not want to read them. The answer can be to turn off the push e-mails so that you only collect the e-mails when you want to.