Etiquette is important in email, just as it is with the rest of life. I have collected here, some of the things that bug me most about emails I receive from people. If you feel like I missed something, bring it up in the comments.
Only sending forwards:
There are, believe it or not, people who still do this. Typically, they send forwards of forwards of forwards (etc.). When I get emails from a fellow human being, I appreciate that person putting some thought into letting me know how they are doing, and actually typing out a message. Most of these just click forward, select the entire address book, and hit send.
If you really want to share something like this with your friends get a blog. Copy. Paste. If your friends want to read it they will. If everyone did this, it would save countless terabytes on email servers around the world, as well as reducing spam. One way spammers get your email address is mass emails that are not sent using the BCC field.
I don't mind the occasional forward from someone who actually talks with me from time to time--but they should not be the norm.
Poor (If Existent) Spelling, Punctuation, and Grammar:
Not everyone is an English Major. That is fine. Just do the best you can. It is very difficult to read anything without punctuation (this includes caps at the beginning of the sentence), using a spell checker is easy enough, and if you can use a computer, and you don't have a handle on grammar--good luck in life. Over-use of smilies and text messaging “words” is out too--they serve a purpose, but I don't want to wade through them in an email.
Come to think of it, over-use of anything gets tiring. It is fine to be casual, just be careful how casual you get.
Giving My Email to a Corporate Entity:
Someone did this to me recently. The amount of spam in my account has tripled. Company A says that if this person gets six people to create accounts, said company will give this person a $600 (US) piece of software (or, an iPod--it varies). That is all well and good, but in order to create an account, one must enter six more email addresses. Its good for the spammer company, not really for anyone else. Inboxes are filled with spam, no one can unsubscribe (not even using the link provided--which is not recommended).
If someone asks you for someone else's email address, its a good idea to know (with at least 90% certainty) how that data will be used. I look at email addresses like I do physical ones. If someone asked me for six of my friends addresses I would laugh in their face. I don't know if I have enemies I would do that to.
The Work Email:
I have friends who frequently write from work. Its fine with me if they do that, but that email goes into the corporation's official record. If you reply to that email at the same address it is not a private conversation. For my part, its not a problem, but I have seen some, um... er... questionable material on coworkers email screens.
I have probably violated each of these rules at different times, but this is the one I have infringed on most. (Though, in my defense, I would have gladly removed anyone from the list who said they wanted off.)
Many people still have dial-up. Think about this before clicking the “Send” button. Do(es) your recipient(s) have a dial-up connection? If so, do you know them well enough to know if they mind waiting 17 minutes to download that 4 MB picture of your mother-in-law asleep in front of the TV (if they want the photo at all)?
One option is to provide a link to the file, which they could download at their discretion. If that is not possible, you could send a short email describing what you want to send them, and ask if they want it.
Etiquette is all about treating other people how they want to be treated. Think about what you are sending, before you send it. Think about your audience. Think about the limitations of their computer and/or bandwidth (for mass emails, use the lowest common denominator).
It does not take a lot of work to think these things through, and when one gets in the habit, it takes even less time. You may not get thanked for your thoughtfulness, but that is not the point.