anchor.diff:  
   These configuration properties can be specified either in `isis.properties` or in an xref:ugbtb.adoc#_ugbtb_deployment_externalized-configuration[external configuration file].
   
  -If prototyping (that is, running the app using `org.apache.isis.WebServer`), the configuration properties can also be specified as system properties. For example, if you create a test email account on gmail, you can configure the service using:
  +If prototyping (that is, running the app using `org.apache.isis.WebServer`), the configuration properties can also be specified as system properties.
  +For example, if you create a test email account on gmail, you can configure the service using:
   
   [source,ini]
   ----
  
positive.code: 
  The `EmailService` provides the ability to send HTML emails, with attachments, to one or more recipients.
  
  Apache Isis provides a default implementation to send emails using an external SMTP provider.  Note that this must be configured (using a number of configuration properties) before it can be used.  The that sends email as an HTML message, using an external SMTP provider.
  
  
  
  
negative.code: 
  == Registering the Services
  
  Assuming that the `configuration-and-annotation` services installer is configured (implicit if using the `AppManifest` to xref:rgcms.adoc#_rgcms_classes_AppManifest-bootstrapping[bootstrap the app]) then Apache Isis' core implementation of `EmailService` service is automatically registered and injected (it is annotated with `@DomainService`) so no further configuration is required.
  
  To use an alternative implementation, use xref:rgant.adoc#_rgant-DomainServiceLayout_menuOrder[`@DomainServiceLayout#menuOrder()`] (as explained in the xref:rgsvc.adoc#_rgsvc_intro_overriding-the-services[introduction] to this guide).
  
  
  == Related Services
  