I may have the not so popular opinion here:

Maybe you misread his flirting. Often times people joke with each other and then build a rapport that is more comfortable than they would otherwise be with co-workers. I for example have a male co-worker who jokes with me regularly. He comes to say hello and see how my weekend was. This may seem as though he is flirting when the underlying truth is that while he is being friendly he is married and very happy. So his being nice could cause some confusion for me if I had feelings for him right? If I take a step back and put things into context he is just being friendly and although he does show that he enjoys my company he isn't necessarily saying that he enjoys it enough to pursue anything more.

Now, lets put things into even better context...you both work together so maybe he does enjoy a little flirting and a deeper friendship that just that of a working relationship but hte fact of the matter is he is a co-worker and maybe he isn't willing to pursue anything for the simple fact that it wouldn't be something he openly goes after (you know dating a co-worker). That is very reasonable actually...what if things went sour? You'd both be very uncomfortable if you were coming out of a failed romantic relationship for the simple fact that you both still have to see each other frequently at work.

Maybe you made him uncomfortable by telling him about your feelings and he is not ready to address whether or not he reciprocates. I personally don't think confronting him as to exactly why he didn't reply is the smart thing to do. If he is already acting a bit strange you may have your answer. He may feel terribly odd knowing you actually have feelings for him if he liked casually flirting with you and wanted nothing more.

See when a man shows you who he is and how he handles things - believe him!

Point in case, you sent him one email hinting that you liked him and he didn't reply. After a while he came around again and acted as he normally did (i.e. the flirting).

After not getting a response from him and him acting as though nothing happened you upped the anty and point blank told him you liked him as more than a co-worker and friend...and he again didn't reply and in fact is now acting odd...

He is showing you that he didn't particularly like or know how to handle the first email. He seemingly just skipped over it thinking that because you were ambiguous about yoru feelings he could go back to the relationship you normally have but then you send a very clear email citing your feelings and that kind of forced him to behave one of two ways:

1) behave as though he reciprocates your feelings and can no longer fly under the radar by flirting with you at work; or

2) behave in a way that is true to his feelings that maybe he enjoyed flirting occasionally but didn't desire anything more - this is tough because now he is forced to either tell you outright that he doesn't share your feelings or simply just stop his flirting immediately as to avoid confusing you further.

Have a bit of empathy for the fella and realized he may also be scared that this is happening at work...

It isn't a reflection of you or your worth it is just simply the age old battle of meeting someone and seeing if there are reciprocated feelings there.