Types of Letters (Purpose? Audience? Style?)
Thank-you letters
Postcards
Letters in newspapers
Letters sent home from school
A character reference
A formal letter of complaint
A short simple note left for someone
A letter asking for information
A letter with details of a special offer
A bill!
A letter confirming something
Notification that something has happened
Your library book has arrived
Your order has arrived
You need to renew your insurance policy/road tax, etc