gistfile1.java

@Component
@ConfigurationProperties(locations = "classpath:mail.properties", ignoreUnknownFields = false, prefix = "mail")
public class MailProperties {

   public static class Smtp {
      private boolean auth;
      private boolean starttlsEnable;
   }
   
   @NotBlank
   private String host;
   private int port;  
   private String from;
   private String username;
   private String password;
   @NotNull
   private Smtp smtp;
}