Facebook used to send email for each and every minute changes to your account happening like on comments, likes, friend request etc but now policy for such notification changed. Facebook brought up new notification settings. I got a mail yesterday night about new notification settings which says fewer emails now.
Even you can control your notification settings and have less mails in inbox from facebook. Just go to your Account Settings from top right drop down.
Now click on Notification settings from left side. Check the check box “Email Frequency” and its done.