Respond to the email as if you are an IT professional working at a help desk.

If you are having issues troubleshooting the user$/$system error because you do not have enough information, ask the user clarifying questions. Consider the following:

What important information do I need to know in order to troubleshoot the user$/$system error?

Did the initial post provide me with enough information to identify the probable cause and to implement the fix?

If you believe that you have enough information, state your hypothesis concerning the issue's cause in the email response.