@Zach: That is fair enough, and my intent was to demonstrate that those familiar and comfortable with the Windows ecosystem may not find SmarterMail on Linux as a benefit. I am comfortable in Windows, Unix, and Linux environments, so moving between them can be trivial.
A word on Linux volume encryption. That is all well and good, but unless it offers limited access to privileged accounts, I would not recommend SmarterTools lean too much upon it as a solution. The same goes for Bitlocker on Windows. The Windows EFS allows user-level encryption, meaning that anyone who is not the user, and who does not have the user's EFS certificate installed, cannot access the user-encrypted files.
In my Post.Office example, no other user on the system which could be compromised will have access to the Post.Office user-encrypted files. Thus, if the machine was to be attacked, access to email storage is prevented (baring a highly sophisticated compromise, which gets deep into the weeds.) As well, if the account's password is changed, the EFS certificate becomes invalidated.
Linux does appear to offer something similar, but I have not yet tried it out. I encourage SmarterTools to explore methods of encrypting the email store, and include management processes into SmarterMail. This will dramatically increase confidence in the software, both as a product and as a service.