From today, users signing up to Google's email service will get an @googlemail.com address. However those that have already signed up will keep their @gmail.com addresses.
The decision follows an 18-month dispute between the US search engine, which has a stock market value of $54.4bn (£31.3bn), and the UK financial research company with a market value of just £3.23m.
In September, Google had to switch its service in Germany to the Googlemail name after a court ruled that a Hamburg-based company had already registered the Gmail name.
IIIR has been using the "G-Mail" name for its Pronet subsidiary's web-based email product since May 2002, two years before Google launched its Gmail web-based service.
Google apparently made settlement offers to IIIR, but none that were deemed reasonable, according to Shane Smith, chairman and chief executive of IIIR.
Nigel Jones, senior European counsel for Google, said that the company decided to change the name to avoid any confusion to Google users. Google's service is free and comes with just over 2.6 gigabytes of storage space.
IIIR is believed to still be looking into its legal options after talks between the companies broke down months ago. With existing Gmail customers able to keep their addresses, IIIR may also continue to argue that the Google service has infringed on the trademark of its own G-Mail service in some 80 countries.
According to Mike Lynd, partner at patent and trademark attorneys, Marks & Clerk, Google's best bet is now to rebrand in Europe as Googlemail.
"While Google has successfully built the Gmail brand in the mind of consumers, it will now be forced, as a result of inadequate IP searching and protection, either to give up, or to substantially curb its use, of its brand.
"My advice to Google would be to cut its losses now and to look at rebranding to Googlemail within the whole of Europe. For other companies, it is a salutary lesson in how not to adopt a new trademark," he said.
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