Arabic term (edited): ��� ���

The traditional structure of the preamble used in Arabic correspondence consists of two parts:

The top part usually identifies the addressee fully by name and title. The wording varies. The wording you cited is one of the common formulations. It could read something like this:

حضرة الأستاذ الكريم سليمان بن داود رئيس شعبة المحاسـبين حفظه الله

The second part serves to transition to the body of the letter, and is usually much shorter. The wording you cite is commonly used. It could read something like:

وبعد
أما بعد
تحية طيبة وبعد
السلام عليكم ورحمة الله وبركاته، وبعد

When we translate a letter thus structured, we keep in mind the standard structure commonly used in the target language. It just happens that in English, the preamble of letters consists of two parts as well:

The first part includes the full name, title, and address (depending on how formal the letter is). It could read something like:

Mr. Edward Jones
Director, Research and Development
Comfort Shoes Incorporated
1111 Montrose Boulevard
Dry Lakes, Texas 70001-0001
USA

(The above is all made up)

The second part, just as in the Arabic counterpart, serves to transition to the main body of the letter, and usually begins with the word "Dear," followed either by the name of the addressee or just "sir," "madam" (sometimes "sirs," "madams," or even a combination).

In short, أما بعد corresponds to the transitional part of the preamble, and therefore is best traslated as "Dear Mr. XYZ" or "Dear sir" followed by a comma. The body of the letter begins in the next paragraph.

Keep in mind that "dear" is merely a traditional courtesy, and does not intimate actual dearness.