您可以使用JavaMail API来处理电子邮件任务。JavaMail API可以在JavaEE包中获得，它的jar可以下载。遗憾的是，它不能直接在Android应用程序中使用，因为它使用的AWT组件在Android中完全不兼容。

你可以在以下位置找到JavaMail的Android端口: http://code.google.com/p/javamail-android/

将jar添加到应用程序并使用SMTP方法

SMTP

使用SMTP是一种方法，其他方法已经指出了如何做到这一点。请注意，在这样做的时候，您完全绕过了内置的邮件应用程序，并且必须提供SMTP服务器的地址、该服务器的用户名和密码，可以在代码中静态地提供，也可以从用户那里查询。

HTTP

另一种方法是使用一个简单的服务器端脚本，比如php，它接受一些URL参数并使用它们发送邮件。这样，您只需要从设备发出一个HTTP请求(使用内置库很容易实现)，而不需要在设备上存储SMTP登录数据。与直接使用SMTP相比，这是一种更间接的方式，但由于从PHP发出HTTP请求和发送邮件非常容易，因此它甚至可能比直接方式更简单。

邮件应用程序

如果邮件将从用户已经在手机上注册的默认邮件帐户发送，则必须采用其他方法。如果你有足够的时间和经验，你可能想要检查Android Email应用程序的源代码，看看它是否提供了一些不需要用户交互就可以发送邮件的入口点(我不知道，但也许有一个)。

也许你甚至可以找到一种方法来查询用户的帐户详细信息(这样你就可以将它们用于SMTP)，尽管我高度怀疑这是可能的，因为这将是一个巨大的安全风险，而Android是建立得相当安全。

你考虑过使用Apache Commons Net吗?从3.3开始，只需要一个jar(您可以使用gradle或maven依赖它)，就完成了:http://blog.dahanne.net/2013/06/17/sending-a-mail-in-java-and-android-with-apache-commons-net/

 Add jar files mail.jar,activation.jar,additionnal.jar

 String sub="Thank you for your online registration" ; 
 Mail m = new Mail("emailid", "password"); 

 String[] toArr = {"ekkatrainfo@gmail.com",sEmailId};
 m.setFrom("ekkatrainfo@gmail.com"); 

     m.setTo(toArr);
     m.setSubject(sub);
    m.setBody(msg);



                     try{


                            if(m.send()) { 

                            } else { 

                            } 
                          } catch(Exception e) { 

                            Log.e("MailApp", "Could not send email", e); 
                          } 

  package com.example.ekktra;

   import java.util.Date;
   import java.util.Properties;

   import javax.activation.CommandMap;
   import javax.activation.DataHandler;
   import javax.activation.DataSource;
   import javax.activation.FileDataSource;
   import javax.activation.MailcapCommandMap;
   import javax.mail.BodyPart;
   import javax.mail.Multipart;
   import javax.mail.PasswordAuthentication;
   import javax.mail.Session;
   import javax.mail.Transport;
   import javax.mail.internet.InternetAddress;
   import javax.mail.internet.MimeBodyPart;
   import javax.mail.internet.MimeMessage;
   import javax.mail.internet.MimeMultipart;

   public class Mail extends javax.mail.Authenticator { 
     private String _user; 
     private String _pass; 

     private String[] _to; 

     private String _from; 

     private String _port; 
     private String _sport; 

     private String _host; 

     private String _subject; 
     private String _body; 

     private boolean _auth; 

     private boolean _debuggable; 

     private Multipart _multipart; 


   public Mail() { 
      _host = "smtp.gmail.com"; // default smtp server 
      _port = "465"; // default smtp port 
      _sport = "465"; // default socketfactory port 

      _user = ""; // username 
      _pass = ""; // password 
      _from = ""; // email sent from 
      _subject = ""; // email subject 
      _body = ""; // email body 

      _debuggable = false; // debug mode on or off - default off 
      _auth = true; // smtp authentication - default on 

      _multipart = new MimeMultipart(); 

      // There is something wrong with MailCap, javamail can not find a handler for the        multipart/mixed part, so this bit needs to be added. 
      MailcapCommandMap mc = (MailcapCommandMap) CommandMap.getDefaultCommandMap(); 
   mc.addMailcap("text/html;; x-java-content-handler=com.sun.mail.handlers.text_html"); 
   mc.addMailcap("text/xml;; x-java-content-handler=com.sun.mail.handlers.text_xml"); 
   mc.addMailcap("text/plain;; x-java-content-  handler=com.sun.mail.handlers.text_plain"); 
   mc.addMailcap("multipart/*;; x-java-content-handler=com.sun.mail.handlers.multipart_mixed"); 
   mc.addMailcap("message/rfc822;; x-java-content- handler=com.sun.mail.handlers.message_rfc822"); 
    CommandMap.setDefaultCommandMap(mc); 
   } 

 public Mail(String user, String pass) { 
  this(); 

  _user = user; 
   _pass = pass; 
 } 

public boolean send() throws Exception { 
   Properties props = _setProperties(); 

  if(!_user.equals("") && !_pass.equals("") && _to.length > 0 && !_from.equals("") &&   !_subject.equals("") /*&& !_body.equals("")*/) { 
    Session session = Session.getInstance(props, this); 

    MimeMessage msg = new MimeMessage(session); 

     msg.setFrom(new InternetAddress(_from)); 

    InternetAddress[] addressTo = new InternetAddress[_to.length]; 
     for (int i = 0; i < _to.length; i++) { 
      addressTo[i] = new InternetAddress(_to[i]); 
    } 
      msg.setRecipients(MimeMessage.RecipientType.TO, addressTo); 

    msg.setSubject(_subject); 
    msg.setSentDate(new Date()); 

  // setup message body 
  BodyPart messageBodyPart = new MimeBodyPart(); 
    messageBodyPart.setText(_body); 
    _multipart.addBodyPart(messageBodyPart); 

     // Put parts in message 
    msg.setContent(_multipart); 

    // send email 
    Transport.send(msg); 

    return true; 
   } else { 
     return false; 
   } 
  } 

   public void addAttachment(String filename) throws Exception { 
    BodyPart messageBodyPart = new MimeBodyPart(); 
    DataSource source = new FileDataSource(filename); 
      messageBodyPart.setDataHandler(new DataHandler(source)); 
    messageBodyPart.setFileName(filename); 

   _multipart.addBodyPart(messageBodyPart); 
 } 

  @Override 
  public PasswordAuthentication getPasswordAuthentication() { 
     return new PasswordAuthentication(_user, _pass); 
  } 

   private Properties _setProperties() { 
   Properties props = new Properties(); 

    props.put("mail.smtp.host", _host); 

  if(_debuggable) { 
    props.put("mail.debug", "true"); 
  } 

  if(_auth) { 
    props.put("mail.smtp.auth", "true"); 
   } 

    props.put("mail.smtp.port", _port); 
    props.put("mail.smtp.socketFactory.port", _sport); 
    props.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory"); 
    props.put("mail.smtp.socketFactory.fallback", "false"); 

    return props; 
   } 

   // the getters and setters 
  public String getBody() { 
   return _body; 
 } 

 public void setBody(String _body) { 
  this._body = _body; 
 }

  public void setTo(String[] toArr) {
     // TODO Auto-generated method stub
    this._to=toArr;
 }

public void setFrom(String string) {
    // TODO Auto-generated method stub
    this._from=string;
}

 public void setSubject(String string) {
    // TODO Auto-generated method stub
    this._subject=string;
  }  


   }

为了帮助那些获得网络主线程异常与SDK目标>9。这是使用droopie的代码上面，但将类似于任何工作。

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();

StrictMode.setThreadPolicy(policy); 

android.os.NetworkOnMainThreadException

您可以如下所示使用AsyncTask

public void onClickMail(View view) {
    new SendEmailAsyncTask().execute();
}

class SendEmailAsyncTask extends AsyncTask <Void, Void, Boolean> {
    Mail m = new Mail("from@gmail.com", "my password");

    public SendEmailAsyncTask() {
        if (BuildConfig.DEBUG) Log.v(SendEmailAsyncTask.class.getName(), "SendEmailAsyncTask()");
        String[] toArr = { "to mail@gmail.com"};
        m.setTo(toArr);
        m.setFrom("from mail@gmail.com");
        m.setSubject("Email from Android");
        m.setBody("body.");
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        if (BuildConfig.DEBUG) Log.v(SendEmailAsyncTask.class.getName(), "doInBackground()");
        try {
            m.send();
            return true;
        } catch (AuthenticationFailedException e) {
            Log.e(SendEmailAsyncTask.class.getName(), "Bad account details");
            e.printStackTrace();
            return false;
        } catch (MessagingException e) {
            Log.e(SendEmailAsyncTask.class.getName(), m.getTo(null) + "failed");
            e.printStackTrace();
            return false;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

对于那些想在2020年与Kotlin一起使用JavaMail的人:

首先:将这些依赖项添加到构建中。gradle文件(官方JavaMail Maven依赖项)

实现“com.sun.mail: android-mail: 1.6.5” 实现“com.sun.mail: android激活:1.6.5”

实现“org.bouncycastle: bcmail-jdk15on: 1.65” 实现“org.jetbrains.kotlinx: kotlinx-coroutines-core: 1.3.7” 实现“org.jetbrains.kotlinx: kotlinx-coroutines-android: 1.3.7”

BouncyCastle是出于安全考虑。

第二步:将这些权限添加到AndroidManifest.xml中

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

第三:当使用SMTP时，创建一个配置文件

object Config {
    const val EMAIL_FROM = "You_Sender_Email@email.com"
    const val PASS_FROM = "Your_Sender_Password"

    const val EMAIL_TO = "Your_Destination_Email@email.com"
}

第四:创建Mailer对象

object Mailer {

init {
    Security.addProvider(BouncyCastleProvider())
}

private fun props(): Properties = Properties().also {
        // Smtp server
        it["mail.smtp.host"] = "smtp.gmail.com"
        // Change when necessary
        it["mail.smtp.auth"] = "true"
        it["mail.smtp.port"] = "465"
        // Easy and fast way to enable ssl in JavaMail
        it["mail.smtp.ssl.enable"] = true
    }

// Dont ever use "getDefaultInstance" like other examples do!
private fun session(emailFrom: String, emailPass: String): Session = Session.getInstance(props(), object : Authenticator() {
    override fun getPasswordAuthentication(): PasswordAuthentication {
        return PasswordAuthentication(emailFrom, emailPass)
    }
})

private fun builtMessage(firstName: String, surName: String): String {
    return """
            <b>Name:</b> $firstName  <br/>
            <b>Surname:</b> $surName <br/>
        """.trimIndent()
}

private fun builtSubject(issue: String, firstName: String, surName: String):String {
    return """
            $issue | $firstName, $surName
        """.trimIndent()
}

private fun sendMessageTo(emailFrom: String, session: Session, message: String, subject: String) {
    try {
        MimeMessage(session).let { mime ->
            mime.setFrom(InternetAddress(emailFrom))
            // Adding receiver
            mime.addRecipient(Message.RecipientType.TO, InternetAddress(Config.EMAIL_TO))
            // Adding subject
            mime.subject = subject
            // Adding message
            mime.setText(message)
            // Set Content of Message to Html if needed
            mime.setContent(message, "text/html")
            // send mail
            Transport.send(mime)
        }

    } catch (e: MessagingException) {
        Log.e("","") // Or use timber, it really doesn't matter
    }
}

fun sendMail(firstName: String, surName: String) {
        // Open a session
        val session = session(Config.EMAIL_FROM, Config.PASSWORD_FROM)

        // Create a message
        val message = builtMessage(firstName, surName)

        // Create subject
        val subject = builtSubject(firstName, surName)

        // Send Email
        CoroutineScope(Dispatchers.IO).launch { sendMessageTo(Config.EMAIL_FROM, session, message, subject) }
}

Note

If you want a more secure way to send your email (and you want a more secure way!), use http as mentioned in the solutions before (I will maybe add it later in this answer) You have to properly check, if the users phone has internet access, otherwise the app will crash. When using gmail, enable "less secure apps" (this will not work, when you gmail has two factors enabled) https://myaccount.google.com/lesssecureapps?pli=1 Some credits belong to: https://medium.com/@chetan.garg36/android-send-mails-not-intent-642d2a71d2ee (he used RxJava for his solution)