Think: Is email the best way to communicate your message? Could it be done better in person?
Purpose: What is the message about? Make this clear in the subject line, and summarise the purpose at the start of the email.
Recipients: Address your message to specific people or categories of people, rather than 'Dear all'. For example: 'To all Heads of Schools' or 'To members of Senior Officers' Group' or 'Dear Professor Bloggs'. Use an appropriate style and form of address, bearing in mind the business relationship and the context. If in doubt, err on the side of formality.
Action? Make it clear whether the communication requires any action, and if so, what the timescale is and where the response should be sent.
Short and Simple! Keep all communications as short, straightforward and clear as possible, using plain, correct English (grammar, spelling, punctuation and proof-reading are important even in emails!)
Copies and history: Copy in others only where necessary, and take care with 'blind copying'. Delete previous email correspondence unless it is essential to understanding. Remember it can contain confidential information or comments which are not for further dissemination.
'Mass' messages to all staff should always be checked and sent by a person of appropriate authority.
Attachments: Hold large documents on the web, and link to them, rather than sending as an attachment.... but check that web-links do work, and that they take readers to the correct part of the document or site. Check the content of attachments, including 'hidden' comments or data, 'track changes' or confidential information.