Hmm, well showing my old-foginess I start with a "signature" saying who I am, website details etc. (Though this is automatically included) Then I use Dear (name) <comma> Dear Humphrey, Then the text - all properly written out and hopefully correctly spelt and punctuated. And I tail it with Regards, Blob (or whatever soubriquet that person knows me by) ........ What's more, I write SMS texts in much the same way !!!
(Nights) Actually most of my emails are no different from letters except in the greeting if I'm familiar with the person. This means capitals, punctuation and paragraphs. Well, why not? At my age you simply don't give a toss if people think you're bizarre. It's great.
The thing is, I tend to see emails as more closely related to memos than letters. When I receive an email written like a formal letter, it comes across, frankly, as somewhat illiterate.