Contents: Salutations | Line Length | Attachments | Format | Subject line Abbreviations | Web links | Discretion - Careful what you say | Terms/Abbreviations/Emoticons

Email Netiquette

Salutations

I've noticed a lot emails I've got recently start with "Hi Don,"
or "Hello," when addressed to multiple people.

webfoot.com says,
Many people do not give either a salutation or a signature. After all, while a letter can get separated from its envelope easily, it is difficult to separate an email message's body from its addressing information. The email message itself says who it is to and from.

However, that information might not be adequate for your needs. It might be difficult to find with some email reading software. It might be unclear or ambiguous. It might be inadequate for telling the receivers just why they are getting that message. Or, it might not convey the proper formality or status cues for your purposes. I did a google search on email salutations and couldn't find any consistent guidelines.

Kaitlin Duck Sherwood says: I usually use a simple "Hi" for people that I already know:
  "Hi - Are you interested in getting together for sushi next week?"

Do We Have to Use Email Salutations?
LegalAndrew says no.

See:
A Beginner's Guide to Effective Email - Greetings and Signatures

Check authenticity before Forwarding email

Look up your message in some of the links at the Hoaxes page before forwarding email which asks you to send it to all your friends.

Line length

Set your email client's automatic word wrapping feature to something between 65 and 75 characters to make sure your messages do look good in every email program on every computer.
Note: It's better to let your mail program wrap than to try and type returns yourself. If you type your own returns at the end of lines and make tham longer than your default line length you will end up with a choppy text with alternating long and short lines.
e.g. If you type:

  Now is the time for all good people to come to the aid of their country.<RETURN>
  A second line after hitting the return key.

Your message will end up like:

Now is the time for all good people to come to the aid of their
country.
A second line after hitting the return key.

see email.about.com/cs/NetiquetteTips

Attachments

Attachments are great for sending things other than text or html. E.g. Word processing documents, spread sheets, pictures, songs, compressed collections of files (.zip)... However, the recipient must have program and correct version to open them, so agree with the recipient about the format of an attachment before you send it.
E.g. some Dell computers shipping in 2004 had Word Perfect instead of MS Office.
Attachments also cause extra steps of download and opening another program to view them, which take up bandwidth, disk space and processing time.
There are size limitation on attachments depending on the mail server you are using (e.g. hotmail, yahoo, comcast, aol, ...)

Here are some tips to consider before attaching a document.

• Title the document that you are attaching in a way that is easy for the recipient to find once he or she downloads it to his or her files. For example, if you are sending a document that is a goal statement then title it "goalstatement.doc."
• In the content of your email, tell your recipient what type of software was used to create the document, the year/version, and the title of the attachment. For example: "The file attached is called "goalstatement.doc" and it is in MSWord 2000."
• Make sure that you do not send overly large attachments unless you are sure that your recipient's Internet connection and email client can handle them. For example, a user on a 56K dialup would have to spend a long time downloading a 5M PowerPoint file, whereas a co-worker on a fast work connection would have no problem.
• Don't send unnecessary attachments -- if you've already presented all of the relevant information in an email message, don't attach a Word document repeating the same information

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An email signature comprises a few lines of text placed at the bottom of all outgoing mail. It can contain your name, website, company, phone number, and even a short elevator pitch or favorite quote.
See Email Signature for more information and ideas.

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Format - Plain Text vs HTML

Some email programs are not capable of rendering the HTML used for rich formatting in email messages. Others try, but fail, rendering your message unaccessible to the recipient. When in doubt send plain text.

BFF   - Best Friends Forever
FCOL  - For Crying out loud
LMFAO - Laugh my Fucking Ass Off
NBD   - No Big Deal
TMI   - Too Much Information
WTF   - Why the face or What the fuck
YMMMV - Your Mileage May Vary

Entire message in the subject line:

Sometimes your entire message will fit in the subject line.  E.g.

Subj: Re: Can you make tomorrows meeting? | Yes, see you tomorrow at 7 PM EOM

EOM - End of Message (11K google hits)
SIM - Subject is Message (5K google hits)
n/t - No Text
NT - No Text
SSIA - Subject says it all
NIM - No internal message
SO - Subject Only

AB: Action by e.g. AB+2 Action by 2 days
AR: Action Required
Action: Action Required
Action Alert: Action Required
Important Important
EOM: or eom or <EOM> at the end - End of Message - Whole message in the Subject line (See above)
FW: Forward - A forwarded message
FYA: For your action
FYI: For your information
NRR: No reply required (same as FYI)
NT: or n/t - No Text - Whole message in the Subject line (See below)
NWS: or NSFW Not Work Safe or Not Safe for Work - Adult content (More below)
RE: Reply - Reply to a message - usually inserted by mail program
RR: Reply Requested
SIM: -Subject is Message - Whole message in the Subject line (See above)
URG: Urgent 
WAS: Old topic changed. e.g., 
"Re: What is the best kind of teapot? (WAS: What is the correct temp. for brewing tea?)"

See List of email subject abbreviations - Wikipedia
Calendar entries:
  Automatic calendar entries from email were around in proprietary systems 30 years ago.
 
  Create automatic calendar entry from gmail  in certain format - Google Groups 
  in Feb 2011 suggests a way to do this with:
  Subject: 20110220, 13:00, 14:00, "Meeting with Manager" 
  Apparently MS Outlook uses "Copy:"
 I'd suggest:
EVENT: 20120303 13:00, 14:00, "Meeting with Manager" 

  
 The following are my suggestions which are sub categories of FYI:
Humor or LOL (Laugh out Loud): Jokes and things like "You know you're getting old if ..."
Cool: Emails with someones beautiful pictures, video links, etc.
WIS: Wisdom - How to save your marriage, How to deal with a liberal/conservative, ...
POL: Political comment/opinion
REL: Religion 

Others:
ADV: Advertising - Proposed by the FTC's 
"Subject Line Labeling As A  Weapon Against Spam"
ACTION: (Air Force Guidance Memorandum - 9 Nov. 2011)

• Thou shalt include a clear and specific subject line.
• Thou shalt edit any quoted text down to the minimum thou needest.
• Thou shalt read thine own message thrice before thou sendest it.
• Thou shalt ponder how thy recipient might react to thy message.
• Thou shalt check thy spelling and thy grammar.
• Thou shalt not curse, flame, spam or USE ALL CAPS.
• Thou shalt not forward any chain letter or virus warning.
• Thou shalt not use e-mail for any illegal or unethical purpose.
• Thou shalt not rely on the privacy of e-mail, especially from work.
• When in doubt, thou shalt save thy message overnight and reread it in the light of the dawn.

Thanks:
If the only thing you have to say is "Thanks" most people do not reply at all to avoid email overload.