The chart above shows the queue of mail waiting to be processed (light green shading) and the number of messages/minutes processed (red line). If the queue is greater than 1000 messages, the chart switches to a logarithmic scale and the queue sampling frequency is reduced to once per five minutes.
There are often messages in the queue for a while, as remote mail servers around the world are not always accessible. Sometimes the destination address is wrong, but our mail system is unable to get a permanent error, and so keeps trying for up to five days.
The chart above shows mail flow (messages/hour) over the previous week. Calendar date is shown on the x-axis.