One of my many hats is that of a Governor to a local Primary School and we just reviewed and updated our "Acceptable Use Policy" for IT part of which was an "Email Etiquette" guide. I thought this part would be useful to a wider audience so I've generalised it and used it below.
1. Know Your Audience
Your e-mail greeting and sign-off should be consistent with the level of respect and formality of the person you're communicating with. Write your emails for the person who will be reading it – if they tend to be very polite and formal, write in that language. The same goes for a receiver who tends to be more informal and relaxed.
If you don't know your audience then it's better to go with the formal approach and let their own responses dictate your approach for future emails. A person expecting an informal email is less likely to be offended by a formal email that a person expecting a formal email is likely to be offended by an email which starts "Yo ..."!
2. Emotions Don't Translate Well
Happiness, anger, etc are very difficult to communicate in an email and are also open to wide interpretation. For example "That's great" - does that mean well done for good work or was that sarcasm?
This goes both ways. Don't assume something you've read and taken personally was intended that way. Pick up the phone, drop by the desk (if possible) and talk to the person. If something is not clear seek clarification - don't jump to conclusions. Cultural background, experience with email, as well as just how busy/rushed that person was at the time! can all feature in an email.
3. Respond In A Timely Fashion
If the email requires a simple acknowledgement (such as "Yes, I understand", or "See you then") then respond quickly, for emails which require a more detailed response then 2 or 3 days might be okay, if an email requires a response then longer than that might cause people to think that their email has been missed or ignored (just dropping the sender back an email saying "I've received your email, I'll have the report for you end of next week" - can help with larger tasks).
4. Be Clear In Your Subject Line
With inboxes being clogged by hundreds of e-mails a day, it's crucial that your subject line gets to the point. It should be reasonably simple and descriptive of what you have written about.
Never open an old e-mail, hit Reply, and send a message that has nothing to do with the previous one. Do not hesitate to change the subject as soon as the thread or content of the e-mail chain changes.
5. Email Attachments
Attachments included in emails should be appropriate to the email message, have meaningful names, and where appropriate use a file format that the recipient(s) are likely able to open (i.e. PDF rather than Word or Excel).
If you're sending a lot of attachments then you might have to split your message up - if that's necessary then try and add something that gives the user an idea how many emails to expect so they know they've got everything (for example "Email 1 of 3 ...").
6. Be Careful With Confidential Information
You are responsible for your own emails. If you need to put confidential information into an email you need to ensure that the recipients are aware that the information is confidential and that they shouldn't then forward it on to other people.
One way to do this is to add "** CONFIDENTIAL **" to the start (not the end) of the email subject.
7. Know When To Stop
Sometimes emails will go back and forth as each recipients attempts to "clarify" something - if you spot this it's best to pick up the phone and have a quick call to clear up any confusion rather than continuing with back-and-forth emails!
8. Keep It Short And To The Point
9. Include An Email Signature
Outlook (and many other email programs) will let you specify an email signature that is automatically attached to all of your emails. This is a very useful feature for including thinking the like the company you work for and your contact details (phone number, website, etc). If you keep this up to date then it works really well.
Outlook will also let you have a different signature when you reply to an email than if you just created a new one - this is useful as it can be much shorter (Name, Mobile number) and won't clog up the conversation with lots of unnecessary detail.
10. Ready To Send?
Always spell check your message (and subject) before sending. Take time to send your messages to the right people (To), people who are interested but aren't required to response are copied in (CC) and people who you want to read the email message but who need to be invisible to other recipients are on the BCC list.
Beware of the "reply all", ask yourself if all the recipients need the information in your message. If they don't, why send it, and if they do should they be included in the reply or forwarded a separate copy.
If your email is high or low priority, remember to set the appropriate flag but overuse of the high priority might lead to people ignoring it.
So that's it. 10 (simple?) points for better email. The key point though for documents like this is to keep them updated and make sure the users, the people who will be following it, have a means of contributing into the next version.
Your e-mail is a reflection of you, in some cases this might even be the first impression someone has of you, with a few simple tricks and attention to detail you can appear professional and get across the message you have to convey.