I emailed every senator yesterday, none of them bounced so I'd guess that you messed up the address for those that did. Email read receipts are unreliable, the recipient must allow the read response, most probably don't, or don't even know about it, having the same result.
So far two have responded (more than I expected on Super Bowl weekend) and both stated opposition to any new gun control, not just this bill.
The general feeling on Northwest Firearms is that it won't pass, the sponsor of this bill does it every year. Still have to be vocal though.
Sent from my Galaxy Nexus that ate your iPhone.