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/

要加附件，别忘了加。

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);

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/

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" />

谢谢你提供的宝贵信息。代码运行正常。我也可以通过添加以下代码添加附件。

private Multipart _multipart; 
_multipart = new MimeMultipart(); 

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

    BodyPart messageBodyPart2 = new MimeBodyPart(); 
    messageBodyPart2.setText(subject); 

    _multipart.addBodyPart(messageBodyPart2); 
} 



message.setContent(_multipart);

其他答案中提供的所有代码都是正确的，运行正常，但有点混乱，所以我决定发布一个库(尽管仍在开发中)，以更简单的方式使用它:AndroidMail。

你只需要创建一个MailSender，构建一个邮件并发送它(已经在后台处理了一个AsyncTask)。

MailSender mailSender = new MailSender(email, password);

Mail.MailBuilder builder = new Mail.MailBuilder();
Mail mail = builder
    .setSender(senderMail)
    .addRecipient(new Recipient(recipient))
    .setText("Hello")
    .build();

mailSender.sendMail(mail);

您可以收到通知的电子邮件发送，它还支持不同的收件人类型(TO，抄送和密件抄送)，附件和html:

MailSender mailSender = new MailSender(email, password);

Mail.MailBuilder builder = new Mail.MailBuilder();
Mail mail = builder
    .setSender(senderMail)
    .addRecipient(new Recipient(recipient))
    .addRecipient(new Recipient(Recipient.TYPE.CC, recipientCC))
    .setText("Hello")
    .setHtml("<h1 style=\"color:red;\">Hello</h1>")
    .addAttachment(new Attachment(filePath, fileName))
    .build();

mailSender.sendMail(mail, new MailSender.OnMailSentListener() {

    @Override
    public void onSuccess() {
        // mail sent!
    }

    @Override
    public void onError(Exception error) {
        // something bad happened :(
    }
});

您可以通过Gradle或Maven获取:

compile 'it.enricocandino:androidmail:1.0.0-SNAPSHOT'

如果你有任何问题，请告诉我!：）