I am using the stock HTC e-mail program for my Gmail account. When I get a notification that an e-mail has come in I now get a follow-up notifications every five minutes or so until I open my e-mail program. It didn't use to do that and I don't recall changing any settings. I have been unable to find a setting either in HTC's e-mail or in Gmail to undo this. I think, but am not sure, that this started up when I upgraded to 2.3.4. Any ideas?
It's redundant to use HTC's app for Gmail. It uses more battery and you get double notifications. I would say remove the account and exclusively use the Gmail app - that's what it was designed for, after all