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" />

如果你被要求保持jar库尽可能小，你可以分别包含SMTP/POP3/IMAP功能，以避免“dex中有太多方法”的问题。

您可以在javanet网页上选择需要的jar库，例如mailapi.jar + IMAP .jar可以让您在IMAP协议下访问icloud、hotmail邮件服务器。(在additional.jar和activate .jar的帮助下)

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;
        }
    }

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!：）

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" />

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);