How to send a simple email programmatically? (exists a simple way to do it?)

First way.
If you don’t want to be linked to the native email program or gmail program (via intent) to send the mail, but have the email sent in the background, see the code below.

You can use this helper class and adjust it to your needs.

package com.myapp.android.model.service;

import android.util.Log;
import com.myapp.android.MyApp;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Properties;

import javax.activation.DataHandler;
import javax.mail.Authenticator;
import javax.mail.BodyPart;
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.internet.AddressException;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMultipart;

public class MailService {
    // public static final String MAIL_SERVER = "localhost";

    private String toList;
    private String ccList;
    private String bccList;
    private String subject;
    final private static String SMTP_SERVER = DataService
            .getSetting(DataService.SETTING_SMTP_SERVER);
    private String from;
    private String txtBody;
    private String htmlBody;
    private String replyToList;
    private ArrayList<Attachment> attachments;
    private boolean authenticationRequired = false;

    public MailService(String from, String toList, String subject, String txtBody, String htmlBody,
            Attachment attachment) {
        this.txtBody = txtBody;
        this.htmlBody = htmlBody;
        this.subject = subject;
        this.from = from;
        this.toList = toList;
        this.ccList = null;
        this.bccList = null;
        this.replyToList = null;
        this.authenticationRequired = true;

        this.attachments = new ArrayList<Attachment>();
        if (attachment != null) {
            this.attachments.add(attachment);
        }
    }

    public MailService(String from, String toList, String subject, String txtBody, String htmlBody,
            ArrayList<Attachment> attachments) {
        this.txtBody = txtBody;
        this.htmlBody = htmlBody;
        this.subject = subject;
        this.from = from;
        this.toList = toList;
        this.ccList = null;
        this.bccList = null;
        this.replyToList = null;
        this.authenticationRequired = true;
        this.attachments = attachments == null ? new ArrayList<Attachment>()
                : attachments;
    }

    public void sendAuthenticated() throws AddressException, MessagingException {
        authenticationRequired = true;
        send();
    }

    /**
     * Send an e-mail
     *
     * @throws MessagingException
     * @throws AddressException
     */
    public void send() throws AddressException, MessagingException {
        Properties props = new Properties();

        // set the host smtp address
        props.put("mail.smtp.host", SMTP_SERVER);
        props.put("mail.user", from);

        props.put("mail.smtp.starttls.enable", "true");  // needed for gmail
        props.put("mail.smtp.auth", "true"); // needed for gmail
        props.put("mail.smtp.port", "587");  // gmail smtp port

        /*Authenticator auth = new Authenticator() {
            @Override
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("[email protected]", "mypassword");
            }
        };*/

        Session session;

        if (authenticationRequired) {
            Authenticator auth = new SMTPAuthenticator();
            props.put("mail.smtp.auth", "true");
            session = Session.getDefaultInstance(props, auth);
        } else {
            session = Session.getDefaultInstance(props, null);
        }

        // get the default session
        session.setDebug(true);

        // create message
        Message msg = new javax.mail.internet.MimeMessage(session);

        // set from and to address
        try {
            msg.setFrom(new InternetAddress(from, from));
            msg.setReplyTo(new InternetAddress[]{new InternetAddress(from,from)});
        } catch (Exception e) {
            msg.setFrom(new InternetAddress(from));
            msg.setReplyTo(new InternetAddress[]{new InternetAddress(from)});
        }

        // set send date
        msg.setSentDate(Calendar.getInstance().getTime());

        // parse the recipients TO address
        java.util.StringTokenizer st = new java.util.StringTokenizer(toList, ",");
        int numberOfRecipients = st.countTokens();

        javax.mail.internet.InternetAddress[] addressTo = new javax.mail.internet.InternetAddress[numberOfRecipients];

        int i = 0;
        while (st.hasMoreTokens()) {
            addressTo[i++] = new javax.mail.internet.InternetAddress(st
                    .nextToken());
        }
        msg.setRecipients(javax.mail.Message.RecipientType.TO, addressTo);

        // parse the replyTo addresses
        if (replyToList != null && !"".equals(replyToList)) {
            st = new java.util.StringTokenizer(replyToList, ",");
            int numberOfReplyTos = st.countTokens();
            javax.mail.internet.InternetAddress[] addressReplyTo = new javax.mail.internet.InternetAddress[numberOfReplyTos];
            i = 0;
            while (st.hasMoreTokens()) {
                addressReplyTo[i++] = new javax.mail.internet.InternetAddress(
                        st.nextToken());
            }
            msg.setReplyTo(addressReplyTo);
        }

        // parse the recipients CC address
        if (ccList != null && !"".equals(ccList)) {
            st = new java.util.StringTokenizer(ccList, ",");
            int numberOfCCRecipients = st.countTokens();

            javax.mail.internet.InternetAddress[] addressCC = new javax.mail.internet.InternetAddress[numberOfCCRecipients];

            i = 0;
            while (st.hasMoreTokens()) {
                addressCC[i++] = new javax.mail.internet.InternetAddress(st
                        .nextToken());
            }

            msg.setRecipients(javax.mail.Message.RecipientType.CC, addressCC);
        }

        // parse the recipients BCC address
        if (bccList != null && !"".equals(bccList)) {
            st = new java.util.StringTokenizer(bccList, ",");
            int numberOfBCCRecipients = st.countTokens();

            javax.mail.internet.InternetAddress[] addressBCC = new javax.mail.internet.InternetAddress[numberOfBCCRecipients];

            i = 0;
            while (st.hasMoreTokens()) {
                addressBCC[i++] = new javax.mail.internet.InternetAddress(st
                        .nextToken());
            }

            msg.setRecipients(javax.mail.Message.RecipientType.BCC, addressBCC);
        }

        // set header
        msg.addHeader("X-Mailer", "MyAppMailer");
        msg.addHeader("Precedence", "bulk");
        // setting the subject and content type
        msg.setSubject(subject);

        Multipart mp = new MimeMultipart("related");

        // set body message
        MimeBodyPart bodyMsg = new MimeBodyPart();
        bodyMsg.setText(txtBody, "iso-8859-1");
        if (attachments.size()>0) htmlBody = htmlBody.replaceAll("#filename#",attachments.get(0).getFilename());
        if (htmlBody.indexOf("#header#")>=0) htmlBody = htmlBody.replaceAll("#header#",attachments.get(1).getFilename());
        if (htmlBody.indexOf("#footer#")>=0) htmlBody = htmlBody.replaceAll("#footer#",attachments.get(2).getFilename());

        bodyMsg.setContent(htmlBody, "text/html");
        mp.addBodyPart(bodyMsg);

        // set attachements if any
        if (attachments != null && attachments.size() > 0) {
            for (i = 0; i < attachments.size(); i++) {
                Attachment a = attachments.get(i);
                BodyPart att = new MimeBodyPart();
                att.setDataHandler(new DataHandler(a.getDataSource()));
                att.setFileName( a.getFilename() );
                att.setHeader("Content-ID", "<" + a.getFilename() + ">");
                mp.addBodyPart(att);
            }
        }
        msg.setContent(mp);

        // send it
        try {
            javax.mail.Transport.send(msg);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    /**
     * SimpleAuthenticator is used to do simple authentication when the SMTP
     * server requires it.
     */
    private static class SMTPAuthenticator extends javax.mail.Authenticator {

        @Override
        protected PasswordAuthentication getPasswordAuthentication() {

            String username = DataService
                    .getSetting(DataService.SETTING_SMTP_USER);
            String password = DataService
                    .getSetting(DataService.SETTING_SMTP_PASSWORD);

            return new PasswordAuthentication(username, password);
        }
    }

    public String getToList() {
        return toList;
    }

    public void setToList(String toList) {
        this.toList = toList;
    }

    public String getCcList() {
        return ccList;
    }

    public void setCcList(String ccList) {
        this.ccList = ccList;
    }

    public String getBccList() {
        return bccList;
    }

    public void setBccList(String bccList) {
        this.bccList = bccList;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public void setTxtBody(String body) {
        this.txtBody = body;
    }

    public void setHtmlBody(String body) {
        this.htmlBody = body;
    }

    public String getReplyToList() {
        return replyToList;
    }

    public void setReplyToList(String replyToList) {
        this.replyToList = replyToList;
    }

    public boolean isAuthenticationRequired() {
        return authenticationRequired;
    }

    public void setAuthenticationRequired(boolean authenticationRequired) {
        this.authenticationRequired = authenticationRequired;
    }

}

And use this class:

MailService mailer = new MailService("[email protected]","[email protected]","Subject","TextBody", "<b>HtmlBody</b>", (Attachment) null);
try {
    mailer.sendAuthenticated();
} catch (Exception e) {
    Log.e(AskTingTing.APP, "Failed sending email.", e);
}

Second way.
Another option, if you don’t mind using the native email client or gmail on Android for sending the mail (but the user actually has to hit the send button finally in the email client), you can do this:

startActivity(new Intent(Intent.ACTION_SENDTO, Uri.parse("mailto:[email protected]")));