A letter generally should have 5 to 7 parts, depending on the type of letter. The common parts include:

1. Heading (date and sender's address)
2. Salutation or Greeting
3. Body (main message of the letter)
4. Closing (a polite ending phrase)
5. Signature (sender's name and signature)

Some letters, especially formal business letters, also include the recipient's address and a complimentary close before the signature, making a total of 7 parts. Friendly letters may also have an optional postscript (P.S.) after the signature. So, a letter typically has between 5 and 7 essential parts for formal letters, and about 6 parts if including the optional postscript in informal letters.