Spring Boot - Example Email with Thymeleaf HTML Templates

I have a Spring Boot backend application that needed to send emails.

Java application email libraries include: Java mail native, Spring, and apache email (and others).  Lots of articles say apache email API is more intuitive, but others say if you are already using a Java/Spring application, then to go ahead and use the Spring one.   I decided to try the Spring Boot one first, since we have a Java/Spring application.

The Spring boot library satisfied the three criteria below, and seems to work great on my local environment:

1. the ability to send simple text email 
2. the ability to send HTML email (support for HTML emails already had the Thymeleaf HTML templating library provided with Spring Boot)
3. the ability to attach a file(s) to the email

The application is using the "Starters" spring boot jars (i.e. spring-boot-starter-web, spring-boot-starter-data-jpa, spring-boot-starter-security, etc), so I just needed to make the application aware of the spring-boot-starter-thymeleaf jar file for the application to use it.

Environment:
Windows 7
Oracle Java 1.8.0_66
Spring Boot 1.3.1.RELEASE
Sprint Boot 1.3.1.RELEASE spring-boot-starter-thymeleaf

The example below supports criteria number 2 to send HTML emails using Thymeleaf email templates.  I've also included unescaped HTML, passing multiple variables to HTML template, and inline image in the example below as well.