We have have the ESA (formerly Ironport) for a number of years. This year when we renewed our licence I noticed that the Cisco licencing group starts the licence (for 3 years in our case) from the date of purchase - not starting on the last day of the end of the previous licence period. We lost 2 months of licence this way.
Just be warned when you do this as it took many weeks to attempt to get the missing months back.
