Islands are named that way because their appearance looks like an island – a time zone infraction in which the middle sticks out above the others. Another term for this pattern is the head-and-shoulders pattern.
Islands are the most ambiguous scenarios because while they indicate that a problem existed in the past, it is more difficult to ascertain that condition now. A drop in outbound spam from the previous hour could mean two things:
- The problem has been resolved and latent spam reports are still trickling in.
- Alternatively, it could mean that there is random, hour-to-hour noise. During the next hour, the problem is easier to diagnose because a different, more telling pattern will form.
Valleys, similar to mountains, generally give very unambiguous signals that a spam problem has occurred. It is usually a very clear signal that a sudden shift in outbound spam has occurred because the current run so greatly dwarfs the previous one.