...
The "Zones" chart type allows you to set up zip code to zip code or zone to zone pairs codes or zones with rates under the Stamp Rate Header tab. See Zones for more information.
...
Click the arrow next to the New button, or press the N key.
Click Stamp Rate Chart.
Under Chart Type select "Zones".
Select the Rate zone.
Go to the Stamp Rate Details tab to enter the zone to zip code or zone rates you would like to use.
Click Apply to save the rate chart and keep it open or click OK to save and close the rate chart.
...