We have Exchange Server 5.5 with SP4 on an NT server with SP4, which is our PDC (primary domain controller). We have a BDC (backup domain controller) in place. Now our PDC is going down every so often due to some internal hardware controller problem. How can we shift this Exchange server onto a new server along with all mailboxes and get them functioning? At this stage we have no plans to go for Windows 2000 domain or Exchange Server 2000.
I would promote the BDC to be the new PDC. Then, if possible, I would make sure the new PDC is running SP6a, plus all critical updates. Then build a new member server running NT4 SP6a or Windows 2000 SP3 (again with all critical updates on both). Install Exchange 5.5 in the same Site/Org as the existing Exchange 5.5 server. Apply SP4 for Exchange. Then use the Move Mailbox option to move the mailboxes to the new server. Re-home the public folders, as well. Also, follow all of the other procedures in How to remove the First Exchange Server in a site.
Leave Exchange running on the old server until all MAPI clients have logged on. This should allow the MAPI clients to get automatically redirected to the new server.
Of course, take a full backup before proceeding with any of this, and update your ERD disks for NT as well. Be sure to have a solid back-off plan in case something goes wrong.