sending mail using external smtp from container

I prepared an app that can send mail through and it works well but, when I run it using docker, I get an error – as it can’t connect to The function sending mails is:

public void sendEmal(String body, String mailRecipient){
   Properties props = new Properties();
   props.put("mail.transport.protocol", "smtp");
   props.put("mail.smtp.auth", "true");
   props.put("", "");
   props.put("mail.smtp.socketFactory.class", "");
   props.put("mail.smtp.port", "465");
        Authenticator auth = new SMTPAuthenticator();
        Session mailSession = Session.getDefaultInstance(props, auth);
        Transport transport = mailSession.getTransport();

        MimeMessage message = new MimeMessage(mailSession);
        message.setContent(body, "text/plain");
        new InternetAddress("mailRecipient"));

    catch(Exception e){

This is the error:

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  • myapp_thirdInst | DEBUG SMTP: trying to connect to host
    “”, port 465, isSSL false

    myapp_thirdInst | javax.mail.MessagingException: Unknown SMTP host:;

    myapp_thirdInst | nested exception is:

    myapp_thirdInst |

    myapp_thirdInst | error sending mail

    It’s the first time I’m playing with docker and after some tries, it continues to fail. I’m kind of lost – could anyone give me a hint to solve this issue?

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  • One Solution collect form web for “sending mail using external smtp from container”

    The first thing you need to do is get DNS working! Test the container DNS first with a shell, get that working and then your SMTP code may work.

    Perhaps you can update your question with information about your DNS configuration

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