Although the punctuation at the end of the salutation in a cover letter is really a minor issue, it is one that has given many people pause. Here are the general rules for punctuation at the end of a salutation:
If you want to be formal in your tone, use the colon (:).
If you want to be informal in your tone, use the comma (,).
Dear Managing Editor:
These rules are true for any correspondence that you have (e.g., emails, letters, etc.)
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