I found a product called Cryoserver.
Sold in US by NY base co.:
http://www.primeviewusa.com/cryoserver.cfm
The product does email archiving with encryption for compliance and forensics.
This an appliance solution. Can support up to 10K email boxes.
I talked to them on Fri and they have plans to do hosting services as well.
They do AES-128 bit encryption.
They also mentioned that a Scalix client in Montana just purchased their solution.
So my guess is they do work with Scalix.
If you only looking for archiving, there are other probably better products.
I'll try to update more after researching additional companies.