All builds of AsyncOS 6.1.* to 7.0.* have reached their End-Of-Life date, and they have been removed from the general available list. If you want to upgrade to a higher version and don't see the proper path available, please contact SecureLink so that Cisco can provision you to the desired AsnycOS version.
This means only following versions are still being supported:
In order to see the official End-Of-Life-Dates and when alert notifications have been sent, please visit http://www.cisco.com/web/ironport/product_discontinuance.html, where you can review the "Announced Software Product Life Cycle" for Cisco IronPort AsyncOS for Email Security.