We've been having that issue as well. We have all in send and receive correct. Here's what works :
Delete all message threads associated with the email address. You and the other person need to do that. Next, toggle off iMessage and FaceTime. Then Reset Network Settings. Go to Settings >General >Reset >Reset Network Settings. Your phone will reboot and you will have to enter your wifi passcode back in. Then toggle iMessage and FaceTime back on. This worked for us. It is an iOS 8 bug.
Sent from my ancient but trustworthy iPhone 5.