Start with both domains pointing at the same content. Easiest way to achieve this is to update your DNS server to point to the same IP / Content area.

Then use a 301 redirect to rewrite inquiries for your old domain to the new domain.

Then you don't have to change anything else.

I have done this with solid results at a current large medical website that used to have three different domains pointing to it. Due to old inbound links with the old URL's this is definately the way to handle this.

Most importantly, leave these redirects in place for at least 6 months, if not permanently based on links to your site from other domains.

By doing this, the engines will update to the new domain name, and you shouldn't lose any of the current traffic you are receiving.

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