Hello,

the external links having a different domain that the original site where the sitemap is generated are by default excluded from the XML sitemap to ensure that it will be a valid sitemap when submitted to Google.

If you have a site for example at this address:
http;//www.mydomain.com

and inside the related XML sitemap you have a link pointing for example to
http;//directory.mydomain.com

you can't include that link into the sitemap generated on http;//www.mydomain.com because Google will throw an error about 'URL not allowed'.

If you want to try i will tell you how to include the link to external directory using a Joomla template override so customizing the output of JSitemap.

Best regards

John Dagelmore