Account setting in Windows Phone "as items arrive"

Account setting in Windows Phone "as items arrive"

Dear all,
I've configured new email account in my Windows Phone 8.1 in active sync and also in IMAP. Do you know why in account settings, I haven't the setting "as items arrive" for download new email? I've only 15-30 minutes, hourly or manually. Any idea about this issue? 

Thanks and regards.