In general, greetings are not capitalized in a sentence, but when used as salutations in email greetings they are capitalized.
You do have the option of only capitalizing the first word in the phrase of a salutation, but the choice is ultimately up to you.
For example, when used at the beginning of an email or as a greeting, the following phrases are capitalized:
- Good Afternoon
- Good Day
- Good Evening
- Good Morning
- Good Night
- To Whom It May Concern
For more capitalization questions, use our free title capitalization tool here.