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);

这里是一个Alt版本，也适用于我，并有附件(已经张贴在上面，但完整的版本不像源链接，人们张贴他们不能让它工作，因为它缺少数据)

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;
  }  

  // more of the getters and setters ….. 
}

在活动中调用它…

@Override 
public void onCreate(Bundle icicle) { 
  super.onCreate(icicle); 
  setContentView(R.layout.main); 

  Button addImage = (Button) findViewById(R.id.send_email); 
  addImage.setOnClickListener(new View.OnClickListener() { 
    public void onClick(View view) { 
      Mail m = new Mail("gmailusername@gmail.com", "password"); 

      String[] toArr = {"bla@bla.com", "lala@lala.com"}; 
      m.setTo(toArr); 
      m.setFrom("wooo@wooo.com"); 
      m.setSubject("This is an email sent using my Mail JavaMail wrapper from an Android device."); 
      m.setBody("Email body."); 

      try { 
        m.addAttachment("/sdcard/filelocation"); 

        if(m.send()) { 
          Toast.makeText(MailApp.this, "Email was sent successfully.", Toast.LENGTH_LONG).show(); 
        } else { 
          Toast.makeText(MailApp.this, "Email was not sent.", Toast.LENGTH_LONG).show(); 
        } 
      } catch(Exception e) { 
        //Toast.makeText(MailApp.this, "There was a problem sending the email.", Toast.LENGTH_LONG).show(); 
        Log.e("MailApp", "Could not send email", e); 
      } 
    } 
  }); 
} 

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/

无法连接到SMTP主机: Smtp.gmail.com，端口:465

在清单中添加这一行:

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

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;
        }
    }

GmailBackground是一个小型库，可以在后台发送电子邮件，无需用户交互:

用法:

    BackgroundMail.newBuilder(this)
            .withUsername("username@gmail.com")
            .withPassword("password12345")
            .withMailto("toemail@gmail.com")
            .withType(BackgroundMail.TYPE_PLAIN)
            .withSubject("this is the subject")
            .withBody("this is the body")
            .withOnSuccessCallback(new BackgroundMail.OnSuccessCallback() {
                @Override
                public void onSuccess() {
                    //do some magic
                }
            })
            .withOnFailCallback(new BackgroundMail.OnFailCallback() {
                @Override
                public void onFail() {
                    //do some magic
                }
            })
            .send();

配置:

repositories {
    // ...
    maven { url "https://jitpack.io" }
 }
 dependencies {
            compile 'com.github.yesidlazaro:GmailBackground:1.2.0'
    }

权限:

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

对于附件，你需要设置READ_EXTERNAL_STORAGE权限:

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

源

(我自己测试过)