My sitemap.xml have a different domain and this is an error I have created a site with a development domain name. Now this site is online (camperlife.it), but sitemap.xml created by XML sitemap module still contains the development domain name. 

I have rebuilt sitemap many times, but without success. 

Where is my problem ?
I think you have a setting wrong.

Browse to the XML Sitemap settings page (admin/config/search/xmlsitemap/settings).

Expand the Advanced Settings section.

Check/set the Default Base URL.  Typically, I set this to make sure the default base URL gets used, as rebuilding from drush won't set it properly if you don't $uri set in your site alias.