Thanks for your enquiry, and sorry for the delay.
Archive encryption (in addition to password protection) and incremental archiving (appending to an existing archive) are features that we do plan to add to Archive To Go. At this stage we anticipate that these features may be available by Q1 2010.
In the meantime, we strongly recommend that you protect archives which contain sensitive information by using generic disk encryption software, eg. TrueCrypt.
On the issue of appending, it may suit your organization to archive periodically, by date range. For example, you could create distinct archives for 2008, 2007, etc. instead of a single archive that is potentially huge and time-consuming to create. While it is not possible to search across multiple distinct archives at present, this is a feature that may be added to the Finder tool. And it’s likely that the incremental archiving feature will be capable of merging several distinct archives into a single archive.
Note: As a rough estimate, it takes around 1 hour to archive 3,500 messages. This rate can vary dramatically, depending on network latency and throughput, disk latency, available RAM and virtual memory, among other factors. We expect that version 2.0 will be substantially faster; at this stage it is likely to be available in Q4 2009.
Regards,
Advansys Support