Netiquette is a combination of the words Internet and etiquette.
Typing in all caps on the internet is considered yelling, and is therefore impolite, unless you are yelling. It is also much harder to read.
If you really hate to capitalize properly, it is MUCH better to type in all lowercase than all uppercase. Note the proper use of capitalization to emphasize the word "much" in the previous sentence.
Many new computer users start to type an email and just keep on going. It ends up to be one long paragraph that goes on for a whole page. Most folks find that difficult to read, and some won't even give it a second look.
Do your readers a favor and separate your main thoughts logically by hitting the "Enter" key twice between paragraphs (this ends up putting one blank line between paragraphs). You're also doing yourself a favor because more folks will read your stuff.
You can add the extra "Enter"s while you are typing, or you can wait till after you're done with your long blob of text. If you wait, just read back over it and click just before a new idea or thought and hit the "Enter" key twice to start a new paragraph there. Reading back over your email is always a good idea anyway, just to pick up spelling/grammar/logic mistakes.
P.S. If you don't use correct punctuation between sentences, it is even more important to separate your thoughts into individual paragraphs.