The rules of email etiquette are not "rules" in the sense that I will come after you if you don't follow them. They are guidelines that help avoid mistakes (like offending someone when you don't mean to) and misunderstandings (like being offended when you're not meant to). These core rules of email etiquette help us communicate better via email.
Did the spam filter eat my message? Spare others this nagging question and let them know you got their email.
Don't clog email systems without permission.
Help make the world less confusing. Try to talk about one subject per message only. For another subject, start a new email.
Comma, colon, hyphen and semicolon — all exist for a reason: they make it easier to understand the intended meaning of a sentence. Don't make life more difficult and possibly less interesting for the recipients of your emails. Pay some — though not too pedantically much — attention to punctuation.
DYK? Not everybody knows every acronym, and they don't save that much time anyway.
When your photos look good in your email, you look good, too! Here's how to make sure your images are not larger than screens and mailboxes by resizing them in style — online and for free.
Don't shout in your emails (and all caps is so difficult to read).
No, really! I mean it. Honestly!
You can often find typos or misplaced commas neither your spell checker nor you yourself catch when proofreading on the screen.
Avoid embarrassing emails by sending them to yourself only (by default).