In the Hudson configuration "Hudson URL" ist set to http://www.foo.net/hudson". If appears tha extended email notification uses the it's seperate "Hudson URL" setting even if "Override Global Settings" is not checked.

If unchecked "Override Global Settings", changes the normal "Hudson URL", but the file "hudson.plugins.emailext.ExtendedEmailPublisher.xml" still contains the the overwrite-setting. This is very confusing, the only way to fix this is activating "Override Global Settings" and the now visible overwrite-"Hudson URL" values.