This worked on my X2, just tested it. Put it on vibrate from my lock screen, and, it played right through a calendar event I had setup. It didn't even vibrate actually.
But, now that I think about it, I don't want to miss calls or anything. I think I'll just deal with the annoyance of occasionally having my music interrupted.
The OPs question was specific to email notifications though, so, maybe someone else will have an answer that will only stop those. I wouldn't mind having just the email notifications stop, but, some other ones are important.