Final answer:
Normally, only the first letter of a last name is capitalized in formal address and writing, but full capitalization might be a personal preference or for specific documents.
Step-by-step explanation:
You would typically capitalize every letter in a person's last name when it is a personal preference or on certain legal documents where it might be required for clarity. However, in formal writing and address, you normally only capitalize the first letter of the last name, unless the individual prefers otherwise or there is a specific style guide you are following that dictates full capitalization. When writing a business or formal letter, address the recipient with their appropriate title, and capitalize proper nouns and titles as they are proper adjectives. If addressing a person by their title such as President, Dr., or Professor, you would use their preferred or highest-ranking title, typically capitalized only in the first letter. Always use parentheses to enclose nonessential information and capitalize the first word of a sentence.