I am frustrated by people I work with (in my own company, not even counting clients and vendors), who exhibit exceptionally poor form with e-mail correspondence. It is not even about whether they reply quickly or not. It is about understanding that e-mail as a vehicle of communication, while fast, is still more akin to writing letters than it is to speaking on the phone or in-person. When you are speaking with someone, you have a direct and immediate ability give and receive feedback from that person. A hesitant pause? You can repeat yourself if it seems they did not understand what you just said. Garbled communication, too much background noise? Ask to repeat as well. Point not understood? Explain in more detail. Something said raises additional issues? Pursue that line of thought. This is not without its drawbacks of course because the instantaneous of the communication can lead to both inane rambling as well as difficulty extricating oneself from the conversation. It is apparently rude to just walk away from someone in the middle of a conversation. Who knew?
E-mail, though fast, is still a form of communication with lag. Therefore, if you are unclear with your message, you force a reply (or risk not getting the correct follow-up). This means e-mails should be clear and specific. Of course, there is a balance to how long and how detailed an e-mail needs to be. At some point, an overly specific message is not efficient. However, most people do not need to worry about including too much information. The opposite problem exists. Sometimes e-mails come in that make me wonder if they were read before they hit 'send'. Your nonsensical gibberish somehow manages to not answer any of my questions nor provide any clear course of expected action. In this case, I have to take the time to write back and ask you to basically re-write your e-mail so that it does not suck. Furthermore, out of some notion of professionalism, I have to phrase my reply politely enough so that you cannot tell how frustrated I am with your sloppy communique.
Related to this, I am particularly boggled by people who provide yes/no answers to either/or questions. In my head, I scream, "but that wasn't a yes/no question!" I have come to assume the person has simply misunderstood or incompletely read the question and is giving a yes/no answer to one of the options. However, when the answer with a singular "yes" or "no" and no further context, it doesn't provide any insight into the exact nature of their poor reading comprehension. Again, a reply is required to request additional clarification.
And no, I almost never read these before I hit "Publish". Of course, I don't work with you and have no expectation that any action be taken upon reading.