First disclaimer, to my knowledge Symantec still does not support the use of Brightmail as a virtual appliance on anything other than VMWare, so proceed at your own risk. Now with that said, if you snapshot your working image before you make any major changes you should be pretty safe.
Over the past few years I have been using the OS restore files to install Brightmail on a physical Dell 2850 server. This process has worked pretty well since the OS restore runs a hardware detection during the setup, the problem was when it came to upgrades more time than not the self-update process would render the system unbootable. It’s always been my desire to run Brightmail as a virtual server since it’s not very load intensive for our mail volume, but the dependence on SCSI boot disk rendered it Hyper-V incompatible. When I read the read me for the most recent version of Brightmail I noticed it listed additional hardware support, so I thought I would give it a try and it was successful.
For my setup I used Symantec_Messaging_Gateway_OSrestore_9.5.3-3_Linux_Int.iso file from Symantec download site. For the most part it’s a straight forward virtual machine setup except for the network adapter, I discovered after the initial install I had no network connectivity, I resolved this by removing the network adapter and adding a “Legacy Network Adapter” in its place. During the initial GUI Bright setup process it detected version 9.5.4, so I had it apply the update, and it was successful so a good sign.