Thanks I also saw the Vibration Intensity setting. However, that doesn't solve my issue. When I unchecked the "vibrate" option in gmail, I expect it not to vibrate whenever I get a new mail. When I have sound on, it doesn't vibrate. But when I have it on silent/vibrate at work, gmail vibrates again for new mails. If I turn the vibration intensity all the way to 0, gmail stops vibrating but so does everything else. I want other apps like whatsapp to vibrate any new alerts. I didn't have this "all-or-nothing" issue before and I found out it was implemented as a feature in 4.2.2 or something.
Seems like gmail is not able to override the "vibration intensity" option when in vibrate mode.