The FAQ says "Server Fault is for Information Technology Professionals needing expert answers related to managing computer systems in a professional capacity", which is not quite the same as "questions from professional sysadmins" and even less the same as "questions from full time sysadmins" (it could be argued that a number of people perform sysadmin tasks in a professional capacity, but amongst other tasks).
I can understand why cPanel can be looked down upon by full time, professional sysadmins, but as far as I understand, it's still a tool for system administration of servers. (I must say I've only seen it once.)
Not every environment requires the same sysadmin needs. Generally, I'd consider cPanel to be more appropriate on ServerFault than on SuperUser. WebMasters.SE may often be a better place, but questions about e-mails and cPanel would be more off-topic there.
It may be on at the "easier" end of the spectrum, in terms of what it can do and who its target users are, but I don't think this implies it's off-topic. System administration can involve a wide range of skills; few master them all (there can be a Linux/Windows divide, for example).
In addition, there are today 485 questions using the cpanel tag, which puts it on page 4 (out of 146) of the most popular tags. 28.5% of these questions are unanswered, which I guess isn't too bad.