Email has replaced many traditional forms of communication, both verbal and written. The writer of an email must remember that their message may be stored permanently, and that there is no such thing as confidentiality in cyberspace.
Delicate communications should therefore be sent by other means, and you must think carefully before hitting 'send' if the message is written in haste or when emotions are running high.
Avoid sarcasm and subtle humour unless you know that the reader will 'get it'. If in doubt, err towards the polite and formal, particularly where you are not well acquainted with the recipient.
Think carefully about using smiley faces, 'kisses' etc. Are these symbols really suitable for the recipient?
Using capital letters looks like shouting and should be avoided. If you want to emphasise something, try underlining or using italics.
Aim to stick as closely as possible to the conventions of traditional letter-writing. Close attention should be paid to spelling and grammar, and the habit of writing in lower case throughout should be avoided.
A well thought-out subject line will ensure that the message gets the attention it deserves.
Emails will often be printed and filed, and therefore close attention must be paid to layout. Again, treating the construction of an email just as you would a 'real' letter is the most effective approach.
Where there is more than one recipient, list them alphabetically or, in the business environment, according to hierarchy. This applies also to the 'cc' line.
Avoid blind copying ('bcc') where possible: instead, forward the original email on to the third party, with a short note explaining any confidentiality. Blind copying is, however, appropriate for distribution lists, for example, where all recipients must remain anonymous.
If you send an email in error, contact the recipient immediately by telephone and ask them to ignore/delete the message.
It is polite to reply to emails promptly - a simple acknowledgement with a promise that you will give the email your full attention at a given later point is preferable to 'sitting on' the message.
Never use email to reply to correspondence or an invitation that was not sent by email or does not supply an email adress as an RSVP option.
There is no replacement for paper and ink; in this day and age where propriety is so often sacrificed for the sake of immediacy, the truly sophisticated correspondent will put pen to paper rather than dashing off a quick email.