What happens to feedback loop when server is down?

I realize this is more of a question for Amazon, but couldn't find answers over there, so wanted to check to see if someone knew off the top of their head :) I'm on EC2 free tier, and once per week or so, it goes down and I need to restart the httpd service (I probably need to upgrade the hosting level, and definitely need some sort of remote monitoring in place, but that's a different story). It may or may not be because I'll get too many simultaneous hits. During the time that it's down, will Amazon re-attempt the SNS delivery? Or is it a 1-way street and there's no notification back to Amazon?

Thanks!