How should I capitalize a salutation in a letter?
The MLA provides style recommendations for research papers. For guidance on how to capitalize salutations addressed to various categories of persons (e.g., religious, governmental, military), consult Merriam-Webster’s Collegiate Dictionary (“Forms of Address”). For categories not covered, such as salutations used to address a group of people (e.g., “To my students”), consult a reference on business-writing or letter-writing conventions.
“Forms of Address.” Merriam-Webster’s Collegiate Dictionary, 11th ed., Merriam-Webster, 2004, pp. 1618–22.