Send email from Spring Boot with JavaMailSender

Before you start

1. Sign in and verify the domain you send from. Viesti accepts a message only when its From address is on a domain verified in your workspace and the envelope sender (MAIL FROM), which most libraries take from the From address, is on the same domain. DNS setup lists the records.
2. Create an API key on the Credentials page of the dashboard. It is shown once. The key is the SMTP password; the username is apikey.

Add the starter

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

With Gradle: implementation 'org.springframework.boot:spring-boot-starter-mail'.

Configure

In src/main/resources/application.properties:

spring.mail.host=smtp.viesti.email
spring.mail.port=587
spring.mail.username=apikey
spring.mail.password=${VIESTI_API_KEY}
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true
spring.mail.properties.mail.smtp.starttls.required=true
spring.mail.properties.mail.smtp.connectiontimeout=5000
spring.mail.properties.mail.smtp.timeout=5000
spring.mail.properties.mail.smtp.writetimeout=5000
app.mail.from=${MAIL_FROM}

Spring resolves ${VIESTI_API_KEY} and ${MAIL_FROM} from environment variables. starttls.enable upgrades the connection; starttls.required makes Jakarta Mail fail instead of continuing without TLS. The timeouts are in milliseconds; Spring Boot's documentation notes that some defaults are infinite.

export VIESTI_API_KEY="mr_your_api_key"
export MAIL_FROM="Acme <[email protected]>"

Send an email

package com.example.demo;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.stereotype.Service;

@Service
public class ReceiptMailer {

    private final JavaMailSender mailSender;
    private final String from;

    public ReceiptMailer(JavaMailSender mailSender, @Value("${app.mail.from}") String from) {
        this.mailSender = mailSender;
        this.from = from;
    }

    public void sendReceipt(String to) {
        SimpleMailMessage message = new SimpleMailMessage();
        message.setFrom(from);
        message.setTo(to);
        message.setSubject("Your receipt");
        message.setText("Thanks for your order.");
        mailSender.send(message);
    }
}

Test it

Add a runner to your application class that sends one message at startup, run the application, and remove the runner once the message shows up on the Activity page:

package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Bean
    CommandLineRunner sendTestEmail(ReceiptMailer mailer) {
        return args -> mailer.sendReceipt("[email protected]");
    }
}

A refusal fails startup with a MailException carrying the server's reply.

Port 465

spring.mail.port=465
spring.mail.ssl.enabled=true

spring.mail.ssl.enabled sets mail.smtp.ssl.enable, so TLS starts before the SMTP greeting. The STARTTLS properties are ignored on a connection that is already encrypted.

Common errors

Replies from Viesti

Whatever the library, its error includes the server's reply. These are the ones caused by your setup or account:

A 250 reply means Viesti accepted the message. Content screening runs before relay; mail it flags is held for review and shows as quarantined on the Activity page.

Next steps

• DNS setup: DKIM, SPF, DMARC and return-path records for your domain.
• SMTP reference: ports, TLS and authentication in detail.
• HTTP API: send the same message as JSON over HTTPS.
• Limits and Bounces: quotas, message size and suppressions.

Properties are from the Spring Boot Sending Email reference and application properties appendix; tested with Spring Boot 4.1.1 and Angus Mail 2.0.5. Checked 26 September 2026.