I have low self esteem issues, so I sometimes feel the same way, but I am starting to now look at it from another perspective, and I use my own self as an example. I am a huge procrastinator and I am always putting things off.. I do the exact same thing that makes me paranoid when others do it to me. So I have now started to look at it that way... I know personally, I will often read an email right before I go to bed, so I will think ok, I'll email them back tomorrow... but then tomorrow comes, I get busy.. get distracted and completely forget. I also sometimes want to wait until I've had time to think of what I want to say in the reply (if it's something of an important matter..) because I feel like my advice or opinion would be of more use if I had some time to really think about what I want to say in my reply. That being said, I'm probably the biggest procrastintor one will ever find.. and also probably one with one of the worst memory! I am notorious for always forgetting to do things. So now when I feel upset if someone doesn't reply back to me, I keep reminding myself about my own situation and that I myself do it too and then I start to feel better and think maybe they also are procrastinators or just really busy or simply forgot. Maybe wait a week or two and email them back with a quick message asking if they had received your email (and you could always say something like that you've been having problems with your emails being sent so was just wondering if it had gotten to them if you don't want them to let on that you're upset about it)..

Hope you feel better and know that you're not alone in feeling this way..