Mail Delivery Statistics Size
At the bottom of Server Statistics page, there is a button for obtaining mail delivery statistics over time.
The "Mail Delivery Statistics Size" setting defines how many points of data you wish to preserve in memory. For example, if your "Mail Delivery Statistics Interval" is one hour, then saving 48 data
points will keep 2 days worth of statistics.
Keeping a larger statistical sample enables you to look further back in time, but it consumes a little more memory, and makes the Mail Delivery Statistics web page larger.