用Kotlin以编程方式发送电子邮件。

简单的电子邮件发送，没有其他所有功能(如附件)。 TLS始终开启 只有1 gradle电子邮件依赖也需要。

我还发现下面这些邮件POP服务非常有用:

https://support.office.com/en-gb/article/pop-and-imap-email-settings-for-outlook-8361e398-8af4-4e97-b147-6c6c4ac95353

使用方法:

    val auth = EmailService.UserPassAuthenticator("you@gmail.com", "yourPassword")
    val to = listOf(InternetAddress("to@email.com"))
    val from = InternetAddress("you@gmail.com")
    val email = EmailService.Email(auth, to, from, "Test Subject", "Hello Body World")
    val emailService = EmailService("smtp.gmail.com", 465)
    
    GlobalScope.launch { // or however you do background threads
        emailService.send(email)
    }

代码:

import java.util.*
import javax.mail.*
import javax.mail.internet.InternetAddress
import javax.mail.internet.MimeBodyPart
import javax.mail.internet.MimeMessage
import javax.mail.internet.MimeMultipart

class EmailService(private val server: String, private val port: Int) {

    data class Email(
        val auth: Authenticator,
        val toList: List<InternetAddress>,
        val from: Address,
        val subject: String,
        val body: String
    )

    class UserPassAuthenticator(private val username: String, private val password: String) : Authenticator() {
        override fun getPasswordAuthentication(): PasswordAuthentication {
            return PasswordAuthentication(username, password)
        }
    }

    fun send(email: Email) {
        val props = Properties()
        props["mail.smtp.auth"] = "true"
        props["mail.user"] = email.from
        props["mail.smtp.host"] = server
        props["mail.smtp.port"] = port
        props["mail.smtp.starttls.enable"] = "true"
        props["mail.smtp.ssl.trust"] = server
        props["mail.mime.charset"] = "UTF-8"
        val msg: Message = MimeMessage(Session.getDefaultInstance(props, email.auth))
        msg.setFrom(email.from)
        msg.sentDate = Calendar.getInstance().time
        msg.setRecipients(Message.RecipientType.TO, email.toList.toTypedArray())
//      msg.setRecipients(Message.RecipientType.CC, email.ccList.toTypedArray())
//      msg.setRecipients(Message.RecipientType.BCC, email.bccList.toTypedArray())
        msg.replyTo = arrayOf(email.from)

        msg.addHeader("X-Mailer", CLIENT_NAME)
        msg.addHeader("Precedence", "bulk")
        msg.subject = email.subject

        msg.setContent(MimeMultipart().apply {
            addBodyPart(MimeBodyPart().apply {
                setText(email.body, "iso-8859-1")
                //setContent(email.htmlBody, "text/html; charset=UTF-8")
            })
        })
        Transport.send(msg)
    }

    companion object {
        const val CLIENT_NAME = "Android StackOverflow programmatic email"
    }
}

Gradle:

dependencies {
    implementation 'com.sun.mail:android-mail:1.6.4'
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.3"
}

安卓清单：

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

用于发送带有附件的邮件..

public class SendAttachment{
                    public static void main(String [] args){ 
             //to address
                    String to="abc@abc.com";//change accordingly
                    //from address
                    final String user="efg@efg.com";//change accordingly
                    final String password="password";//change accordingly 
                     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); 
                  //1) get the session object   
                  Properties properties = System.getProperties();
                  properties.put("mail.smtp.port", "465"); 
                  properties.put("mail.smtp.host", "smtp.gmail.com");
                    properties.put("mail.smtp.socketFactory.port", "465");
                    properties.put("mail.smtp.socketFactory.class",
                            "javax.net.ssl.SSLSocketFactory");
                    properties.put("mail.smtp.auth", "true");
                    properties.put("mail.smtp.port", "465");

                  Session session = Session.getDefaultInstance(properties,
                   new javax.mail.Authenticator() {
                   protected PasswordAuthentication getPasswordAuthentication() {
                   return new PasswordAuthentication(user,password);
                   }
                  });

                  //2) compose message   
                  try{ 
                    MimeMessage message = new MimeMessage(session);
                    message.setFrom(new InternetAddress(user));
                    message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));
                    message.setSubject("Hii"); 
                    //3) create MimeBodyPart object and set your message content    
                    BodyPart messageBodyPart1 = new MimeBodyPart();
                    messageBodyPart1.setText("How is This"); 
                    //4) create new MimeBodyPart object and set DataHandler object to this object    
                    MimeBodyPart messageBodyPart2 = new MimeBodyPart();
                //Location of file to be attached
                    String filename = Environment.getExternalStorageDirectory().getPath()+"/R2832.zip";//change accordingly
                    DataSource source = new FileDataSource(filename);
                    messageBodyPart2.setDataHandler(new DataHandler(source));
                    messageBodyPart2.setFileName("Hello"); 
                    //5) create Multipart object and add MimeBodyPart objects to this object    
                    Multipart multipart = new MimeMultipart();
                    multipart.addBodyPart(messageBodyPart1);
                    multipart.addBodyPart(messageBodyPart2); 
                    //6) set the multiplart object to the message object
                    message.setContent(multipart ); 
                    //7) send message 
                    Transport.send(message); 
                   System.out.println("MESSAGE SENT....");
                   }catch (MessagingException ex) {ex.printStackTrace();}
                  }
                }

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

无需用户干预，您可以按以下方式发送:

从客户端apk发送电子邮件。这里mail.jar，激活。jar是发送java电子邮件所必需的。如果添加这些罐子，它可能会增加APK大小。 或者，您可以在服务器端代码中使用web服务，它将使用相同的mail.jar和activation.jar发送电子邮件。你可以通过asynctask调用web服务并发送电子邮件。参考相同的链接。

(但是，您需要知道邮件帐户的凭据)

如果使用“smtp.gmail.com”作为默认的smtp服务器，请注意。

谷歌将迫使您更改您的链接电子邮件帐户密码频繁由于他们过于热心的“可疑活动”政策。本质上，它将短时间内来自不同国家的重复smtp请求视为“可疑活动”。因为他们假设你(电子邮件账户持有人)一次只能在一个国家。

当谷歌系统检测到“可疑活动”时，它将阻止进一步的电子邮件，直到您更改密码。因为你已经将密码硬编码到应用程序中，每次发生这种情况，你都必须重新发布应用程序，这并不理想。这种情况发生在一周内3次对我来说，我甚至存储密码在另一个服务器上，每次谷歌强迫我更改密码时，我都动态地获取密码。

因此，我建议使用许多免费的smtp提供商之一，而不是“smtp.gmail.com”，以避免这个安全问题。使用相同的代码，但将“smtp.gmail.com”更改为新的smtp转发主机。

在Android中使用JavaMail API使用Gmail身份验证发送电子邮件。

创建示例项目的步骤:

MailSenderActivity.java:

public class MailSenderActivity extends Activity {
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        final Button send = (Button) this.findViewById(R.id.send);
        send.setOnClickListener(new View.OnClickListener() {
            
            public void onClick(View v) {
                try {   
                    GMailSender sender = new GMailSender("username@gmail.com", "password");
                    sender.sendMail("This is Subject",   
                            "This is Body",   
                            "user@gmail.com",   
                            "user@yahoo.com");   
                } catch (Exception e) {   
                    Log.e("SendMail", e.getMessage(), e);   
                } 
                
            }
        });
        
    }
}

GMailSender.java:

public class GMailSender extends javax.mail.Authenticator {   
    private String mailhost = "smtp.gmail.com";   
    private String user;   
    private String password;   
    private Session session;   
  
    static {   
        Security.addProvider(new com.provider.JSSEProvider());   
    }  
  
    public GMailSender(String user, String password) {   
        this.user = user;   
        this.password = password;   
  
        Properties props = new Properties();   
        props.setProperty("mail.transport.protocol", "smtp");   
        props.setProperty("mail.host", mailhost);   
        props.put("mail.smtp.auth", "true");   
        props.put("mail.smtp.port", "465");   
        props.put("mail.smtp.socketFactory.port", "465");   
        props.put("mail.smtp.socketFactory.class",   
                "javax.net.ssl.SSLSocketFactory");   
        props.put("mail.smtp.socketFactory.fallback", "false");   
        props.setProperty("mail.smtp.quitwait", "false");   
  
        session = Session.getDefaultInstance(props, this);   
    }   
  
    protected PasswordAuthentication getPasswordAuthentication() {   
        return new PasswordAuthentication(user, password);   
    }   
  
    public synchronized void sendMail(String subject, String body, String sender, String recipients) throws Exception {   
        try{
        MimeMessage message = new MimeMessage(session);   
        DataHandler handler = new DataHandler(new ByteArrayDataSource(body.getBytes(), "text/plain"));   
        message.setSender(new InternetAddress(sender));   
        message.setSubject(subject);   
        message.setDataHandler(handler);   
        if (recipients.indexOf(',') > 0)   
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(recipients));   
        else  
            message.setRecipient(Message.RecipientType.TO, new InternetAddress(recipients));   
        Transport.send(message);   
        }catch(Exception e){
            
        }
    }   
  
    public class ByteArrayDataSource implements DataSource {   
        private byte[] data;   
        private String type;   
  
        public ByteArrayDataSource(byte[] data, String type) {   
            super();   
            this.data = data;   
            this.type = type;   
        }   
  
        public ByteArrayDataSource(byte[] data) {   
            super();   
            this.data = data;   
        }   
  
        public void setType(String type) {   
            this.type = type;   
        }   
  
        public String getContentType() {   
            if (type == null)   
                return "application/octet-stream";   
            else  
                return type;   
        }   
  
        public InputStream getInputStream() throws IOException {   
            return new ByteArrayInputStream(data);   
        }   
  
        public String getName() {   
            return "ByteArrayDataSource";   
        }   
  
        public OutputStream getOutputStream() throws IOException {   
            throw new IOException("Not Supported");   
        }   
    }   
}  

JSSEProvider.java:

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/**
 * @author Alexander Y. Kleymenov
 * @version $Revision$
 */


import java.security.AccessController;
import java.security.Provider;

public final class JSSEProvider extends Provider {

    public JSSEProvider() {
        super("HarmonyJSSE", 1.0, "Harmony JSSE Provider");
        AccessController.doPrivileged(new java.security.PrivilegedAction<Void>() {
            public Void run() {
                put("SSLContext.TLS",
                        "org.apache.harmony.xnet.provider.jsse.SSLContextImpl");
                put("Alg.Alias.SSLContext.TLSv1", "TLS");
                put("KeyManagerFactory.X509",
                        "org.apache.harmony.xnet.provider.jsse.KeyManagerFactoryImpl");
                put("TrustManagerFactory.X509",
                        "org.apache.harmony.xnet.provider.jsse.TrustManagerFactoryImpl");
                return null;
            }
        });
    }
}

将下面链接中的3个罐子添加到你的Android项目中

mail.jar activation.jar additional.jar

点击这里-如何添加外部罐子

别忘了在你的清单上加上这一行:

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

只需点击下面的链接，更改帐户访问不太安全的应用程序 https://www.google.com/settings/security/lesssecureapps

运行项目并检查收件人邮件帐户。

另外，别忘了你不能在android的任何活动中进行网络操作。 因此，建议使用AsyncTask或IntentService来避免主线程网络异常。

Jar文件:https://code.google.com/archive/p/javamail-android/