Question About PROMOX Mail Gateway

Hi,

I'am newbe in here. i have a question, is posible promox mail gateway using previously installed mail server?
i already have dedicated mail server running using centos 6.4 and with latest postfix.

i was looking at documentation, it should remove all harddrive, and install promox mail gateway.
is there posible to use promox mail gateway without loosing all data on harddrive?

Thanks