Are you referring to the presence of $config['fifth_mail']? That's normal. On some servers, you need to change its value to '1' to get the email functionality to work.
The text description in this case is misleading, since that variable is known to the base UBB.threads package, and has nothing to do with hacks or modifications.
The variable was added in that area as a quick fix, rather than adding a distinct checkbox for setting it.
