Whilst it appears higher ranks tend to send email downwards and lower ranks upward for a more detailed view it is possible to plot, for each rank, to which other ranks email is being sent. The plots are shown below:
Looking at these plots it can be seen ranks 0-4 send more email to the rank below than any other; ranks 5-7 send more email to the same rank than any other and only 8 sends more upwards (mostly to 6 and7). It can also be observed that the ranks to which email is sent are fairly tightly packed around the sending rank. Without other organisations to observe it difficult to make sweeping generic statements but I think this shows a lack of ‘mobility’ between the ranks and suggests a command-and-control mentality.