Changes to envoy notification mailing behaviour:

 - Trap failure of "ERROR ON ENVOY" mail and fallback to log Dumper
 - Clear users' notification in all cases, since a problematic one can
   cause the whole queue to get stuck, never clear.

The error log fallback *should* be temporary, to figure out what's
actually going on with the "ERROR ON ENVOY" mail, but nothing persists
like a temporary solution - need to keep an eye on it.
Filling a user mgmt script gap.