January 27, 2006
Recently, someone asked me about moving from one domain to another. He had read that Google recommends using a 301 redirect to let Googlebot know about the move, but he wasn't sure if he should do that. He wondered if Googlebot would follow the 301 to the new site, see that it contained the same content as the pages already indexed from the old site, and think it was duplicate content (and therefore not index it). He wondered if a 302 redirect would be a better option.
I told him that a 301 redirect was exactly what he should do. A 302 redirect tells Googlebot that the move is temporary and that Google should continue to index the old domain. A 301 redirect tells Googlebot that the move is permanent and that Google should start indexing the new domain instead. Googlebot won't see the new site as duplicate content, but as moved content. And that's exactly what someone who is changing domains wants.
He also wondered how long it would take for the new site to show up in Google search results. He thought that a new site could take longer to index than new pages of an existing site. I told him that if he noticed that it took a while for a new site to be indexed, it was generally because it took Googlebot a while to learn about the new site. Googlebot learns about new pages to crawl by following links from other pages and from Sitemaps. If Googlebot already knows about a site, it generally finds out about new pages on that site quickly, since the site links to the new pages.
I told him that by using a 301 to redirect Googlebot from the old domain to the new one and by submitting a Sitemap for the new domain, Googlebot could much more quickly learn about the new domain than it might otherwise. He could also let other sites that link to him know about the domain change so they could update their links.
The crawling and indexing processes are completely automated, so I couldn't tell him exactly when the domain would start showing up in results. But letting Googlebot know about the site (using a 301 redirect and a Sitemap) is an important first step in that process.