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)

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)

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)

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)

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);