Why I get a "Relay not allowed" error when trying to send emails from my java app?

[ghevge]

I have a stelwart mail server configured and I'm able to send and receive emails to/from gmail, when I use thunderbird.

But when I try to send an email from my java app using jakarta library, I get errors like:

2024-08-07T13:21:38Z INFO SMTP MAIL FROM command (smtp.mail-from) listenerId = "smtp", protocol = smtp, remoteIp = <my ip>, remotePort = 42670, from = "test2@mydomain.com"
2024-08-07T13:21:38Z INFO Relay not allowed (smtp.relay-not-allowed) listenerId = "smtp", protocol = smtp, remoteIp = <my ip>, remotePort = 42670, to = "mygmailaddress@gmail.com"

Any idea what am I missing ?

My java send email code looks like this:

private void init() {
        Properties props = new Properties();
        props.put(MAIL_SMTP_AUTH, appConfigs.getMailSmtpAuth());
        props.put(MAIL_SMTP_HOST, appConfigs.getMailSmtpHost());
        props.put(MAIL_SMTP_PORT, appConfigs.getMailSmtpPort());

        // Add a valid EHLO domain
        props.put(MAIL_SMTP_DOMAIN, appConfigs.getMailDomain());
        
        // Enable STARTTLS for secure connection if using port 587
        props.put(MAIL_SMTP_STARTTLS, appConfigs.getMailSmtpTls());
        // create the Session object
        session = Session.getInstance(props, new jakarta.mail.Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(appConfigs.getMailUsername(), appConfigs.getMailPassword());
            }
        });
    }
	
	
	 public void sendMessage(String title, String toEmail, String fromEmail, String textMessage) {
        try {
            Message message = new MimeMessage(getSession());
            message.setFrom(new InternetAddress(fromEmail));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(toEmail));
            message.setSubject(title);
            message.setContent(textMessage, "text/html; charset=utf-8");
            
            Transport.send(message);
        } catch (MessagingException e) {
            log.error("Failed to send email from:" + fromEmail + " to:" + toEmail + " title:" + title);
            throw new RuntimeException(e);
        }
    }

Thanks

[ghevge]

With the same code I am able to send emails to other email addresses within my domain . The error only shows up when I try to send outside of my domain

[ghevge]

I've found a solution to my problem, under /settings/smtp-in-rcpt/edit I've set the Allow Relaying last field to true

[exkc]

DONT DO THAT MAKE YOUR SERVER INTO A OPEN RELAY