In the process of replacing our existing NW6.0 SP5 BM36 SP2 server with new
hardware running NW6.5 SP5 BM38 SP5.

The plan, as recommended by Cat and Craig, is to install and run the new box
in parallel with the old one and give it a thorough testing before taking
the plunge and adding the private IP address of the old server as a
secondary IP to the new box.

Just one question.

The existing server has a secondary mailgate public IP address used to
static NAT to our internal Groupwise7 SMTP server. Is it "SAFE" to add this
existing public IP address to the new server whilst both boxes are running
in parallel? I don't want to screw up our Groupwise system.

Thanks in advance.