For an email-based help desk, keyword extraction and text classification are highly applicable. Keyword extraction can help identify important terms and phrases in emails for quicker routing and response. Text classification can help in categorizing the emails based on their content, thus improving efficiency in handling and prioritizing issues. Structured data analytics and image classification are not applicable as the data is in email text format, while speech recognition is not relevant for email-based systems, and entity extraction, though useful, is less critical compared to keyword extraction and text classification in this context.