When creating a mail account, at the end you can click on "Options" and within this area you can specify if you want the account to send and receive after a certain amount of time.

But, I also noticed that once an account is created, if you go to menu -> Delivery Preferences there is also an option in there to check for messages after a certain amount of time. But, this option is NOT checked by default.

So my question is... which one should I set? Should I set the one from within the mail account or the one from the Delivery Preferences section in the menu?