It makes me feel really awkward... as if I do not know why that person even sent me this in the first place. The ones that bug me the most are the ones that tell me if I don't send it to more people, I will die at midnight or anything like that. At those moments, I ask myself, does my friend really want want me to send this to other people? Why would he or she send me this anyway, without a word?
But this is what I would do, and this is what I would not do.
I wouldn't block my friend though. I would confront and message him or her about my feelings, and how serious I feel when they send me these e-mails without a word. I would ask them why, and request them not to. They may stop, and they may also explain.
But it is also important to understand that they may have no bad intentions. Maybe they just want to joke around with you, and they had no time to leave any other messages. Try to find and sort things out by confronting them, and not by deleting the messages and blocking your friends. This is my advice though, this is what I would do.
Hope this helps. Feel free to message me with any other concerns.