You could just put the phone in airplane mode while in church. That would solve the problems.
In the meantime, I believe you can set up some contacts to ring through the vibration setting. That could be the issue. It's only email, or is it text or mms messages as well?
It is kind of funny, when you hold the power button down to get the restart menu, there is a option there to change volume profiles between sound, vibrate and mute. If you choose vibrate, it will mute the ringtone, notification and system, but not the media volume on the device, leaving that at its previous state.
Are you using a custom ringtone or sound for some email contacts? I could see a tune playing if it needs to play through the media player.
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