A subject line is not really necessary. You may want to use one, however, so that the reader immediately knows what your letter is about. There are three common methods to distinguish the subject line from the body of the letter:
- Use "Subject:" or "Re:"
- Type the subject in bold letters
- Type the subject in capital letters
The subject line is usually placed between the salutation and the body of the letter (with a blank line in between).
In American English, the subject line can also be placed between the recipient's address and the salutation (with a blank line in between).