anchor.diff:  
   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.
  +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.
   
   
   
  
positive.code: 
  If you wish to write an alternative implementation, be aware that it should process the message body as HTML (as opposed to plain text or any other format).
  
  Also, note that (unlike most Apache Isis domain services) the implementation is also instantiated and injected by Google Guice. This is because `EmailService` is used as part of the xref:ugvw.adoc#_ugvw_features_user-registration[user registration] functionality and is used by Wicket pages that are accessed outside of the usual Apache Isis runtime. This implies a couple of additional constraints:
  
  * first, implementation class should also be annotated with `@com.google.inject.Singleton`
  * second, there may not be any Apache Isis session running. (If necessary, one can be created on the fly using `IsisContext.doInSession(...)`)
  
  To ensure that your alternative implementation takes the place of the default implementation, register it explicitly in `isis.properties`.
  
  
negative.code: 
  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:
  
  [source,ini]
  ----
  