public class TesteJavaMais {

    public static void main(String[] args) throws MessagingException {

        final String username = "contato@sirleneimoveis.com.br";
        final String password = "ferrari07H";
        Properties props = new Properties();

        props.put("mail.smtp.host", "smtp.proemail.cloud");
        props.put("mail.smtp.socketFactory.port", "465");
        props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        props.put("mail.smtp.auth", "true");
        props.put("mail.smtp.port", "587");
        props.put("mail.smtp.starttls.enable", "true");

        Session session = Session.getInstance(props,
                new javax.mail.Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication(username, password);
            }
        });

        Multipart multipart = new MimeMultipart();
        MimeBodyPart attachment0 = new MimeBodyPart();
        attachment0.setContent("teste", "text/html; charset=UTF-8");
        multipart.addBodyPart(attachment0);
        MimeBodyPart attachment1 = new MimeBodyPart();
        multipart.addBodyPart(attachment1);
        Message message = new MimeMessage(session);
        message.setFrom(new InternetAddress(username));
        message.setRecipients(Message.RecipientType.TO,
                InternetAddress.parse("joaovithor.gv@gmail.com"));
        message.setSubject("Testing Subject");
        message.setText("Dear Mail Crawler,"
                + "nn No spam to my email, please!");
        //      Transport.send(message);
        message.setContent(multipart);
        Transport.send(message);
    }

    public static boolean validEmail(String email) {
        System.out.println("Metodo de validacao de email");
        Pattern p = Pattern.compile("^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$");
        Matcher m = p.matcher(email);
        if (m.find()) {
            System.out.println("O email " + email + " e valido");
            return true;
        } else {
            System.out.println("O E-mail " + email + " é inválido");
            return false;
        }
    }
}

Exception in thread "main" javax.mail.MessagingException: Could not connect to SMTP host: smtp.proemail.cloud, port: 587;
  nested exception is:
    javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1934)
    at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:638)
    at javax.mail.Service.connect(Service.java:317)
    at javax.mail.Service.connect(Service.java:176)
    at javax.mail.Service.connect(Service.java:125)
    at javax.mail.Transport.send0(Transport.java:194)
    at javax.mail.Transport.send(Transport.java:124)
    at testejavamais.TesteJavaMais.main(TesteJavaMais.java:64)
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
    at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1949)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:302)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:296)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1509)
    at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:216)
    at sun.security.ssl.Handshaker.processLoop(Handshaker.java:979)
    at sun.security.ssl.Handshaker.process_record(Handshaker.java:914)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1062)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1375)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1403)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1387)
    at com.sun.mail.util.SocketFetcher.configureSSLSocket(SocketFetcher.java:507)
    at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:238)
    at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1900)
    ... 7 more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:387)
    at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
    at sun.security.validator.Validator.validate(Validator.java:260)
    at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229)
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1491)
    ... 17 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:382)
    ... 23 more
C:Usersjoao2DesktopTesteJavaMaisnbprojectbuild-impl.xml:1051: The following error occurred while executing this line:
C:Usersjoao2DesktopTesteJavaMaisnbprojectbuild-impl.xml:805: Java returned: 1