Jenkins bug reporting (this site) the label from the plugin is email-ext-template
Git Hub uses email-ext-template-plugin https://github.com/jenkinsci/email-ext-template-plugin
Jenkins lists the name as emailext-template http://jenkins-ci.org/plugin/emailext-template/
plugin repo uses emailext-template http://updates.jenkins-ci.org/download/plugins/emailext-template/0.1-beta/

To avoid confusion I would think they would all use the same name?