Generally my students have been quite pleased about using Email and have told me how much they appreciate knowing they can Email me and know they aren't disturbing me when they do it. I have also been aware that some students, especially at the beginning of the term, find it easier to communicate via Email as there is a bit of anonymity to it. It is very hard to train people about the etiquette that surrounds any form of communication. The etiquette of Email is quite different from written letters or telephone. Mis-spellings or typos are readily accepted and often expected.
Messages often carry no salutations.
It's common to ask for a message to be resent when someone has inadvertently deleted it. Using the reply form of sending a message means that you can include parts of the original message and so not need to reply in full sentences. Trying to be funny is discouraged because it is so difficult over this medium. Junk mail is a real no no. It is a distinct advantage to be confident in your own Email use before you start using it with students.