What is the required configuration steps to have a Spring Boot application send simple e-mails via AWS SES?

You may try below steps to fix your issue. I tried these changes in the forked repo from you and it works for me.

1. Add dependency "com.amazonaws:aws-java-sdk-ses" in pom.xml file.
2. Create an auto configuration class to configure the mail sender bean. Below is example. The AWSCredentialsProvider is configured and provided by spring-cloud-starter-aws out-of-the-box.

.

@Configuration
public class SimpleMailAutoConfig {

    @Bean
    public AmazonSimpleEmailService amazonSimpleEmailService(AWSCredentialsProvider credentialsProvider) {
        return AmazonSimpleEmailServiceClientBuilder.standard()
                .withCredentials(credentialsProvider)
                // Replace US_WEST_2 with the AWS Region you're using for
                // Amazon SES.
                .withRegion(Regions.US_WEST_2).build();
    }

    @Bean
    public MailSender mailSender(AmazonSimpleEmailService ses) {
        return new SimpleEmailServiceMailSender(ses);
    }
}

3. Use spring API to send mail using the configured mail sender.

Hope it helps.

Edit:

If you need to use JavaMailSender instead of MailSender (for instance when you want to send attachments), simply configure SimpleEmailServiceJavaMailSender instead of SimpleEmailServiceMailSender.

Like this:

    @Bean
    public JavaMailSender mailSender(AmazonSimpleEmailService ses) {
        return new SimpleEmailServiceJavaMailSender(ses);
    }

I used AWS SES in a Spring Boot web project some time ago, but I haven't used Spring Cloud AWS to integrate my application with the mail service.

Instead I simply included spring-boot-starter-mail among the project dependencies (pom.xml):

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-mail</artifactId>
</dependency>

Then I set SMTP server parameters in my application.properties. In my case I used these properties:

spring.mail.host=email-smtp.eu-west-1.amazonaws.com
spring.mail.port=465
spring.mail.protocol=smtps
spring.mail.smtps.auth=true
spring.mail.smtp.ssl.enable=true
spring.mail.username=<my-user>
spring.mail.password=<my-password>

Note: server host and port may vary.

Spring Boot will create a default JavaMailSender instance, configuring it with the previos parametes. You can use this object to send emails...

Probably this in not the best approach to AWS SES integration with a Spring Boot application, but it works fine for me.