In business letters nowadays, there are two styles of punctuation being used. One is mixed punctuation and the other is open punctuation.
Mixed punctuation requires a colon to follow the opening salutation and comma to end the complementary close. In open punctuation, both the colon and the comma can be given a miss. This style is popular in the United States and it's also gaining popularity in Europe.
Open punctuation is a relatively new concept in English grammar and has been popularized by the use of computers. It involves a minimal use of punctuation throughout the body of the letter. Due to the ability to review spelling and grammar content electronically, the open punctuation style has become more and more accepted.
Examples of open punctuation include JT Doe PhD instead of J.T. Doe, Ph.D., Sincerely instead of Sincerely, and so on. Basically, you will not use periods in acronyms, abbreviations or times of the day. Don't add commas unless it's necessary.
If you prefer a more conventional style, consider using mixed punctuation. This letter format s the bridge between open and closed punctuation. You will add a colon after the salutation and a comma after the closing line. For example, you may use Dear Mr. Frazier: as the salutation and Sincerely, (your name) as the closing line.
Punctuation in the Address Line
Traditionally, after each address line, a comma is used. Over the past years, open punctuation has become increasingly popular in full block business letters. In this style, there is usually no punctuation at the end of the address lines.
Each line of the address can be left without punctuation. However, if you like the traditional style better, you can use a comma on each line of address except for the last one, which is the more modern style of writing addresses on formal letters.
Punctuation in an U.S. Business Letter
The traditional United States rules for writing business letters state that a colon should be used after the salutation greeting of the business letter; a comma should be used after the complementary close. This style is known as mixed punctuation. However, most businesses prefer open punctuation, which is becoming a norm.
Punctuation in an European Business Letter
In Europe, a comma is traditionally used both after the initial salutation greeting as well as the complementary close in all business letters. Like in the U.S., open punctuation has started to be accepted here as well.
Punctuation in the Body
For block formats, or formats in which each line begins from the left margin, the layout has been modified slightly. The body of the letter is kept justified and a blank line is left between each paragraph. The punctuation in the body of the letter should be followed as the grammar and syntax dictate.
The context of the body remains largely the same, with an opening statement of purpose and subsequent paragraphs stating the background and supporting information. Here, open punctuation is not used.
Newer versions of Microsoft Office have business letter templates where the writing style uses mostly open punctuation. For example, Microsoft Office 2000 offers three types of business letter wizards that can be used to write the letters of your choice. All of these follow different styles and rules of punctuation.