We are in the process of planning an Exchange 5.5 to 2003 Migration just one 5.5 server to a new 2003 server on new hardware. We have all the plans drawn out but an interesting question came up today. After we complete the migration move mailbox's, public folders, change router Calculater etc. We will decomission the 5.5 server at this point for firewall reasons can we assign the former 5.5 server's IP to the new 2003 box. As long as we make the changes in DNS and WINS I see no problem's. Can anyone think of possible propblems?