Gateway Email Encryption compliance

Hi,

We're considering Gateway Email Encryption solution to manage our email encryption with third parties. What I would like to know does this solution meet our requirements? The requirements are as follows:

1. Public key encrypted emails must be exchanged between us and third party
2. PGP Public keys must be exchanged between organisations for encryption (meaning no symmetric or per-email keys to be used)
3. Centralised Key management
4. Must be third party vendor agnostic (ability to communicate with any third party organisation’s Public key)
5. Must support:
   1. Secure (using encryption) shared mailbox in secure way
   2. Secure (using encryption) single (personal) mailbox
   3. Mobile devices
6. Private Key must not be held on end-point devices i.e. Laptops or PCs
7. Must be scalable, highly-available

If these requirements can't be met with this solution, is there a solution that supports all of these?

Kind regards,
Igor