Sometimes it may be useful to indicate the despatch method to be used, such as: Recorded Delivery, Registered Post, Airmail, or Courier Delivery. Type this in capitals at the top left of the letter; a pre-printed sticky label may be used instead.
PRIVATE AND CONFIDENTIAL / CLASSIFICATION LINE
If your letter is personal and/or confidential, indicate this at the top left of the letter and, more important, on the envelope, in cases where the letter is intended to be read only by the addressee.
Use ‘personal’ if the letter must be opened by the recipient only; a ‘confidential’ letter may be opened by his or her deputy but should, of course, be treated confidentially. ‘personal and confidential’ may be used together if it is imperative that only the recipient opens the letter and acts upon it. The words are usually typed in capital letters and/or underlined.
There are many variations of this phrase, e.g. Confidential, Strictly confidential, but little difference in meaning.
SUBJECT TITLE / SUBJECT LINE
A subject title at the beginning of a letter, directly after the salutation, provides a further reference, saves introducing the subject in the first paragraph, immediately draws attention to the topic of the letter, and allows the writer to refer to it throughout. It should be short and concise and should match that given by your correspondent if you are continuing discussion of the same topic. The subject heading
The final letter below shows some further features of a business letter.