Description: An index capable of representing an Enhanced Mail System Status Code. Enhanced Mail System Status Codes are defined in RFC 1893. These codes have the form

class.subject.detail

Here 'class' is either 2, 4, or 5 and both 'subject' and 'detail' are integers in the range 0..999. Given a status code the corresponding index value is defined to be ((class * 1000) + subject) * 1000 + detail. Both SMTP error response codes and X.400 reason and diagnostic codes can be mapped into these codes, resulting in a namespace

capable of describing most error conditions a mail system encounters in a generic yet detailed way.