Tune Postfix alerting thresholds
    
    - improve values based off data gathered in the last three days
      to make alerts more meaningful, especially for mx*.i.o.o and
      mailman3
    - add comments for better understanding and readability
    - anchor existing regex patterns for more precise matching
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>