1) The Heading (usually contains the return address. If necessary, there will be an email, phone number, fax, something similar)
2) The Inside Address (the address of who you're sending this to)
3) The Greeting (aka the salutation. Something like: dear or hello, etc)
4) The Body (the message you're writing)
5) The Complimentary Close (a short, polite closing)
6) The Signature Line (sign name of who wrote it)