Inventory the current site
List important pages, downloads, forms and integrations. Record the domain, DNS and email arrangements separately. Ask content owners which addresses are used in printed materials or external links.
Give old addresses a deliberate destination
Where a page has a suitable replacement, map the old address to that page. Permanent redirects such as 301 and 308 signal a lasting move. Do not send unrelated missing pages to the homepage merely to hide an error.
Verify the journeys after release
Check representative old links and the new navigation through the public domain. Confirm that contact forms reach the intended recipient and that the normal content-editing process still works. Keep the previous release and configuration available according to the agreed rollback plan.