Need to assign Public IPs to a VirtualBox VM

I have a dedicated block of IP Addresses here (32 IPs) and have a windows server running on one of them. Virtual box is installed and works well withits DHCP Served address from the Virtual Host Manager 10.1.200/24 for the VMs. I'm fining myself now needing to expost a VM with a public address for email server and some other services - trying to get rid of an OLD (ancient Ubuntu 12x) server with a new Ubuntu 18 VM system. Its VERY low load and use.
32 bit Intel(R) Xeon(TM) CPU 2.40GHz so not alot of horepower needed and 2GB RAM. The windows box is 64-bit 16GB RAM and 4 Cores (8 logical procs Intel i7 at 3.2GHz).

What do I need to  do to Virtual Box to let it work with real addresses and not the DHCP Assigned ones from Host Manager? I'm sure its simple buit I haven't been able to locate the answer.

THank you,