Problem Context: The goal is to parse emails to extract certain pieces of information and output this in a structured JSON format. Clarity and specificity in the prompt design will ensure higher accuracy in the LLM's responses.

Explanation of Options:

Option A: Provides a general guideline but lacks an example, which helps an LLM understand the exact format expected.

Option B: Includes a clear instruction and a specific example of the output format. Providing an example is crucial as it helps set the pattern and format in which the information should be structured, leading to more accurate results.

Option C: Does not specify that the output should be in JSON format, thus not meeting the requirement.

Option D: While it correctly asks for JSON format, it lacks an example that would guide the LLM on how to structure the JSON correctly.

Therefore, Option B is optimal as it not only specifies the required format but also illustrates it with an example, enhancing the likelihood of accurate extraction and formatting by the LLM.