There are three types of email messages you will compose: sending a new piece of email conversation you start yourself, which we'll cover in this tutorial, emails to which you reply, and forwarded emails. But they all involve your typing some text for the recipient's eyes, so this tutorial will benefit from information relevant to all these cases.
Before we delve in the topic, your reflex should become "Do I need to send this email?" 21st century humans are as busy as it gets without getting an aneurysm, and "information overflow" has its clear share of the blame. In a professional setting, we recommend that you skip sending any email message unless vitally important, or until you have gathered several questions or comments that you can send as a single message. This is your first email etiquette rule of thumb when it comes to clicking that "Send" button!
Most of these bullet points will be discussed in more details in their respective tutorial, but here are a few tips that will keep your emails welcomed by recipients; most problems in the workplace (and personal lives!) come from lack of clear communication; if your email recipients don't even want to open your emails, the battle is lost in advance!
Tip: surveys consistently show that only about half the time spent at work is actually productive; every email received is an assault on that already dismal record.
Work with your email program set to "Offline Mode" to access your messages without being disturbed by new, incoming mail. Go online when you are ready to send and receive emails (write a list of messages to write as you think of them, and centralize email management into a single task).
Unless you are writing an email newsletter, avoid using custom formatting or including pictures in your email; the shorter and simpler, the better. Don't use underlined text except for links; emphasizing words and expressions with boldface or italic is quite OK (notice that we did not say "sentences" or "paragraphs"). Avoid font sizes smaller than 12 pixels or 11 points - how small text will appear ultimately depends on monitor size (including handheld devices like smartphones) and the device's current screen resolution.
As far as font colors go, you will never go wrong with black, the default text setting in all email programs we've ever tested; ideally keep your text monochromatic (a single text color per message). If you have to use another color, pick a dark one, which will (hopefully) be easily legible even to those with impaired vision or low monitor quality.
About font family: not everyone reading your emails will necessarily have the font you chose installed on their computer, in which case they'll see it in a default font over which you have no control. Keeping the default font for your email program will often be best, but there are "web safe fonts" you can use that will nearly always be installed on others' machine; our Email Marketing Tutorial will soon include a web font primer to help you pick these.
Tip: unless you own a kindergarten or a clown promotion agency, avoid using "Comic Sans MS" in your emails.
After having learned the hard way, either sending a message to the wrong recipient, or accidentally clicking the "Send" button prematurely, here's a technique we use: whether you are composing a new email, forwarding or replying to one, erase the destination email addresses and add them at the very end - this makes it impossible to send that message by accidentally hitting "Ctrl+Enter" on your keyboard (standard keyboard shortcut on Windows to send a message), instead of "Enter" for a new line / paragraph.
For extremely important emails (a proposal to a prospect, a request for an interview with your boss, or particular sensitive replies to a client), we recommend copying the text of your final draft, pasting it into a new message, and sending it to another device you own (cell phone, laptop, tablet PC/iPad, etc.) You will be amazed at the number of mistakes you catch proofreading on another device that you missed after proofreading on your main screen!
Caution: treat every email you write as though you were being recorded (practically speaking, they are). Never say anything about someone you would not feel comfortable telling them to their face, and only write things you would not mind saying in front of your parents, spouse, or kids. Email etiquette is a way of being, not just a way of doing.
Another trend consistently exposed in business research shows that most promotions and most sales happen because of the good relationship between parties involved; so, always be positive or constructive in your emails!