Examples

Sending

Clear e-mail address

Subject line completed

Writing etiquette

Examples

Avoid heavy messages

Do not forward chainmail

A series of examples, from the unacceptable to the perfectly appropriate. These were e-mail messages sent in by students to their language teacher. (Readers should bear in mind that French students are little familiar with situations of correspondence with their teachers, whether in paper or electronic form):

Here, the message in French (despite well-established conventions with the teacher it was sent to) has no capitalized words where required, minimal salutations and no complimentary close. The sender virtually defecated his note to his teacher.

This is somewhat nicer, but there is still no capitalization where required (not even on the sender's first name), and no appropriate ponctuation. The complimentary close is very careless, given the obvious student / teacher context.

Again a very informal opening, with virtually no capitals, while the use of abbreviations and non-capitalized words, quite acceptable in on-a-par communication, is here completely out-of-place.
Also, a spell-checker would be advisable.

Apart from over-abundant exclamation marks, and the somewhat too casual tone, this is a relatively polite and courteous message, which respects layout conventions of separating salutations and complimentary closes from the body of the message.

This is fine. The spelling and capitalization are right, the layout clear —although all paragraphs could have been aligned left.
The tone is perfectly appropriate.

Beginners have a well-intentioned tendency to relay chain mail. Never do that. Ever. Chain mails come in a variety of forms.

You have the phoney virus alert category, with a lot of exclamation marks claiming that this new form of virus is going to destroy your hard disk and the like. Rest assured that real viruses never get publicized before it is too late, when whole systems have collapsed under the attack. When in doubt as to the validity of an alert, go http://www.learnstuff.com/learn-stuff-about-hoaxes/, a site that specializes in detecting the valid from the canard.

Another category is humanitarian causes, such as the Plight of Afghan Women or Help Land Mine Victims. These are very well-written and designed to draw the attention of the compassionate among our apprentice surfers.

Yet another, the luck chain, is a better-known sort, that which brings disasters on you and your loved ones should you fail to forward the message to your whole address-book.

All of these of course, are rubbish, but of an insiduous sort. There are two types of vandals operating on the web. One, the more intelligent, create real viruses that wreak havok in systems worldwide. Another, the lesser-gifted, try to get newcomers to generate their own chaos.
See how it works:

You receive one message and send, say, thirty. See what you get after only three stages from your initial forwarding. This is exponential growth. And though the resources of the web are vast, they are not infinite so this evidently slows down the network. Now imagine what happens when you get a chain mail that contains, say, a slideshow about the benefits of Zen meditation. You compile exponential growth with heavy content.

Here, the message in French (despite well-established conventions with the teacher it was sent to) has no capitalized words where required, minimal salutations and no complimentary close. The sender virtually defecated his note to his teacher.
This is somewhat nicer, but there is still no capitalization where required (not even on the sender's first name), and no appropriate ponctuation. The complimentary close is very careless, given the obvious student / teacher context.
Again a very informal opening, with virtually no capitals, while the use of abbreviations and non-capitalized words, quite acceptable in on-a-par communication, is here completely out-of-place. Also, a spell-checker would be advisable.
Apart from over-abundant exclamation marks, and the somewhat too casual tone, this is a relatively polite and courteous message, which respects layout conventions of separating salutations and complimentary closes from the body of the message.
This is fine. The spelling and capitalization are right, the layout clear —although all paragraphs could have been aligned left. The tone is perfectly appropriate.