When responding to any cryptic emails, make sure to have a clear subject line. Only a catchy and relevant subject line will entice the reader to open the email rather than delete it. By offering a nice subject line, the reader will be able to recall it and read it again in the future. This will help them decide whether or not they want to reply to your email. It is very important to write a personal response to a cryptic email. You should always start with a brief but sincere sentence that shows you understand their concern/problem. For example, "I was concerned to read that [your problem] had an impact on your performance." Be sure to include all the information needed for them to solve their issue. If possible, provide a link to more information or a page on your site where they can find an answer to their question. You should never just send another email asking for more details or trying to sell them something. Your readers are kind of annoyed by these emails and may even report you for spamming. Instead, try writing another helpful email when they've given you more information or solved their own issue. This will show that you're interested in what they have to say and that you're here to help whenever they need you. This will make them feel like partners who can trust you with their business.