Hold that message
When writing a difficult or sensitive message, I'll often draft it by hand or in a different application, such as Tex-Edit Plus. I recommend this practice, which protects me from myself.
Here's another nifty trick to outwit that twitching digit. If replying to a difficult e-mail, temporarily delete the 'To:' address and paste it back ony when you are confident your reply is satisfactory. Ridiculous? Works for me.
Your organisation should have a style guide. The trouble is, e-mail feels less like a letter than a friendly chat, where style guides don't apply.
At the very least, use complete sentences. And please use complete words, as they appear in the dictionary. Why write myst abbrvs 2 yr bz cstmrs? Surely it doesn't save any time. Txting is a completely different medium, and even then, skipping vowels is for kids. (Grown-up mobile phones have predictive text with vowels supplied.)
Your professional reputation is at stake when you do business by e-mail, so always double-check what you have written, and never send an e-mail in anger or haste. Ancient e-mails that you have deleted can be retrieved from your computer and used as evidence in court. What you write in an e-mail has as much legal significance as the contents of a paper letter.
E-mail is as public as the Web
Forwarding is just too easy.
Before you click Send, just ask yourself: 'What if someone else reads this?' Your boss. Your competitor. The media. Your team mates. Your spouse. Does it still seem OK? If not, don't send it.
To forward another person's business e-mail usually requires permission from the sender. Issues of privacy and confidentiality should loom large but are often ignored.
With just one little click you can forward an e-mail to thousands. It's very tempting. Does the message seem amusing? relevant? useful? That's no excuse. Remember that your organisation's e-mail system is a business tool. With mindless forwarding you can damage your organisation's reputation and possibly even break the law.
When sending one e-mail to two or more people, you shouldn't automatically reveal all the addresses, which in itself can be a breach of privacy. 'Cc:' is where you list e-mail addresses legitimately shared, like those of your colleagues. For other situations, list addresses under 'Bcc:' (meaning blind carbon copies). Then recipients see only their own address.
Above all, be courteous
In an e-mail, without facial or vocal cues, a joke can seem like an insult. Presumably that is why the smiley face is so popular. :-) means 'Don't get upset, I'm saying this in a friendly voice.'
If your words are courteous, you won't need the smiley, which is often too casual for a business e-mail. If you are really worried about how your message comes across, why not pick up the phone instead?
As you see, there are many reasons to pause before hitting Send.