Despite the name, emails are not letters. Many people try to equate the two, but they are completely different mediums, and different rules have historically applied.
In former times many people had very limited bandwidth and email storage capacity, and would in fact get annoyed (if not downright hostile) with people who put large amounts of unnessecary information in an email. This includes salutations (which are redundant with the email's automatically attached header), and excessive or unnessecary signature/footer information. Return contact information used to be common in footers, just in case it got somehow mangled in the email header. However, it has always been considered common etiquette (aka: "netiquette") to keep footers to 4 lines or less. A lot of this has been formalized in RFC 1855 (section 2.1.1 is for email).
These days those issues are by-and-large moot. However, getting right to the point, and quitting when you are done, are still considered better form that adding a whole lot of polite chuff around the meat of your conversation.
For further detail, you may consider picking up a copy of The Elements of E-Mail Style, although it is about 20 years old, so it may be a bit dated.