Casual Voice is the most laid back of these three styles of writing (and, unfortunately, the most commonly used by people even when not appropriate). When using a casual voice, your writing style may directly reflect how you speak. You might use contractions and address your email recipient by first name (rather than by title with a surname). Additionally, most formal writing conventions are usually ignored. This style is most appropriate for personal emails to friends or family members.

Semi-formal Voice blends the nonchalant manner of the casual style with just the right amount of assertiveness required by splashes of formality. If you decide to use this style be careful. Do not get too personal, stay away from unsuitable comments or jokes, and stick to the business of the email message. And, above all, be consistent, constantly focusing on the message you want to get across. If you are not comfortable with using a full-fledge formal style of writing, but the content of the email necessitates a more than casual approach, then the semi-formal voice is the perfect choice for you. Semi-formal writing is appropriate for personal emails to friends or family members when discussing topics of a serious or business-related nature. It is also definitely applicable to email exchanges with familiar colleagues in work-related discussions, or when responding to customer inquiries with which a trusted business relationship is already firmly established.

Formal Voice is, perhaps, the most strict of these three voices. It has its own traditional set of standards that must be followed. These standards, or rules, include professional salutations to email recipients (no calling your email recipient by first name here), use of complete sentences, no abbreviations, all words are completely spelled out (meaning no contractions allowed), etc. The formal method of writing is most appropriate for job applications, emails of introduction, discussions of a serious or legal nature, and emails to superiors or subordinates. This is also the safest style to use when the email is of a business (or otherwise serious) nature and the recipient of the email is not someone who is familiar to you.