Many sites do not use facilities available in the HTTP protocol correctly, which often has no impact on users, but can have a dramatic impact on the value a machine can derive from the site.

The first common problem is the use of old-fashioned “meta refresh” tags to direct users from one page to another. While these work, search engines will not follow them.

A better solution would be to use standard HTTP response codes:

• HTTP 301 “Content Moved” – This should be used to direct someone to a replacement URL for the content they were attempting to access. Search engines will remember this and will visit the new URL from that point on
• HTTP 302 “Temporarily relocated” – This should be used in general situations where a page has moved temporarily, or you are redirecting based on some decision that you would not want the client to cache

Using the correct HTTP redirection code is critical for search engines. If a page has moved and visitors are directed to the new location with a 302 response, search engines will continue to direct visitors to the old address.

Also, if your site needs to move to a new domain name, it is best to use a permanent 301 redirection of pages on the old domain to the new one, so the new domain comes up in search results instead of the old one.

For more information: http://www.e.govt.nz/resources/research/SEO.pdf