JavaMail API on Android

Question

I'm trying to send an email on Android using the JavaMail API, it's just a simple test

But whenever I try to launch the app, this exception pops up

2020-09-23 13:23:42.442 21860-21971/ae.ucg.mailtest E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-2
    Process: ae.ucg.mailtest, PID: 21860
    java.lang.VerifyError: Rejecting class com.sun.mail.handlers.text_plain that attempts to sub-type erroneous class com.sun.mail.handlers.handler_base (declaration of 'com.sun.mail.handlers.text_plain' appears in /data/app/~~nyiEJPyVs6-ADHqg-ebklA==/ae.ucg.mailtest-_Q4dGJfXP_9F5CZNfhDVtQ==/base.apk)
        at java.lang.Class.newInstance(Native Method)
        at javax.activation.MailcapCommandMap.getDataContentHandler(MailcapCommandMap.java:601)
        at javax.activation.MailcapCommandMap.createDataContentHandler(MailcapCommandMap.java:555)
        at javax.activation.DataHandler.getDataContentHandler(DataHandler.java:597)
        at javax.activation.DataHandler.writeTo(DataHandler.java:299)
        at javax.mail.internet.MimeUtility.getEncoding(MimeUtility.java:316)
        at javax.mail.internet.MimeBodyPart.updateHeaders(MimeBodyPart.java:1551)
        at javax.mail.internet.MimeMessage.updateHeaders(MimeMessage.java:2238)
        at javax.mail.internet.MimeMessage.saveChanges(MimeMessage.java:2198)
        at javax.mail.Transport.send(Transport.java:99)
        at ae.ucg.mailtest.MainActivity$onCreate$1.invokeSuspend(MainActivity.kt:38)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:738)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678)
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665)
     Caused by: java.lang.VerifyError: Verifier rejected class com.sun.mail.handlers.handler_base: java.awt.datatransfer.DataFlavor[] com.sun.mail.handlers.handler_base.getTransferDataFlavors() failed to verify: java.awt.datatransfer.DataFlavor[] com.sun.mail.handlers.handler_base.getTransferDataFlavors(): [0x4]  can't resolve returned type 'Unresolved Reference: java.awt.datatransfer.DataFlavor[]' or 'Reference: javax.activation.ActivationDataFlavor[]' (declaration of 'com.sun.mail.handlers.handler_base' appears in /data/app/~~nyiEJPyVs6-ADHqg-ebklA==/ae.ucg.mailtest-_Q4dGJfXP_9F5CZNfhDVtQ==/base.apk)
        at java.lang.Class.newInstance(Native Method) 
        at javax.activation.MailcapCommandMap.getDataContentHandler(MailcapCommandMap.java:601) 
        at javax.activation.MailcapCommandMap.createDataContentHandler(MailcapCommandMap.java:555) 
        at javax.activation.DataHandler.getDataContentHandler(DataHandler.java:597) 
        at javax.activation.DataHandler.writeTo(DataHandler.java:299) 
        at javax.mail.internet.MimeUtility.getEncoding(MimeUtility.java:316) 
        at javax.mail.internet.MimeBodyPart.updateHeaders(MimeBodyPart.java:1551) 
        at javax.mail.internet.MimeMessage.updateHeaders(MimeMessage.java:2238) 
        at javax.mail.internet.MimeMessage.saveChanges(MimeMessage.java:2198) 
        at javax.mail.Transport.send(Transport.java:99) 
        at ae.ucg.mailtest.MainActivity$onCreate$1.invokeSuspend(MainActivity.kt:38) 
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) 
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:738) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665) 

I'm aware something is wrong in the library itself, but what exactly am I supposed to do?

This is my code

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        lifecycleScope.launch(Dispatchers.IO) {
            try {
                val props = Properties().apply {
                    this["mail.smtp.host"] = "smtp.gmail.com"
                    this["mail.smtp.socketFactory.port"] = "465"
                    this["mail.smtp.socketFactory.class"] = "javax.net.ssl.SSLSocketFactory"
                    this["mail.smtp.auth"] = "true"
                    this["mail.smtp.port"] = "465"
                }

                val session = Session.getDefaultInstance(props, object : Authenticator() {
                    override fun getPasswordAuthentication() = PasswordAuthentication(Config.EMAIL, Config.PASSWORD)
                })

                val message = MimeMessage(session).apply {
                    setFrom(InternetAddress(Config.EMAIL))
                    addRecipient(Message.RecipientType.TO, InternetAddress("..."))
                    subject = "Hello world"
                    setText("This is a hello world message", "UTF-8")
                }
                Transport.send(message)
            } catch (e: Exception) {
                Toast.makeText(this@MainActivity, e.message, Toast.LENGTH_LONG).show()
            }
        }
    }

And this is the library I'm using

implementation 'com.sun.mail:android-mail:1.6.5'
implementation 'com.sun.mail:android-activation:1.6.5'

Answer 1

Apparently is this bug only on SDK level 30 (Android 11) and Google Admins are saying it's a feature... But here I found a solution

Use this in build.gradle:

android {
    ...
    packagingOptions {
        exclude 'META-INF/NOTICE.md'
        exclude 'META-INF/LICENSE.md'
    }
}

dependencies {
    implementation 'com.sun.mail:android-mail:1.6.6'
    implementation 'com.sun.mail:android-activation:1.6.6'
    ...
}

credit to this issue

Answer 2

I ran into the same issue and there were a couple of things to note in order to resolve it:

1. As other's (radda, and this answer) have mentioned, there's a Google Issue Tracker Issue that covers and provides why this issue is happening:

API level 30 adds a new (verifier) feature that verifies that all referenced code actually exists - or fails a build.

2. Even in fixing the issue - by referencing and ensuring you're providing the referenced code (by, for instance, updating the dependencies to the latest - which at this time are 1.6.7); you'll find a build still throws a relatively straight forward complaint:

To resolve (and get up-to-date):

1. If you were providing the libraries manually via /app/libs/mail.jar, /app/libs/activation.jar, and /app/libs/additionnal.jar - you can go ahead and remove them; both google() and maven() repositories are enabled in Android projects - so simply add;

to your project-level gradle file (/build.gradle):

buildscript {
    ext {
        // ...
        java_mail_version = "1.6.7"
    }
    // ...
}

// ...

to your app/module-level gradle file (/app/build.gradle):

    //...
dependencies {
    // ...

    // Dumb Email Sending
    implementation "com.sun.mail:android-mail:$java_mail_version"

    // REMOVE THESE - DEPS WILL DOWNLOAD AUTOMATICALLY
    //implementation 'com.sun.mail:android-activation:1.6.7' // from 1.6.4
    //implementation 'com.sun.mail:android-additionnal:1.6.7' // from 1.6.4
}

// ...

...and with that you'll have resolved the 'latest version(s)' issue once and for all (including where to find them).

To resolve issue #2, add;

to that same app/module-level gradle file (/app/build.gradle):

// ...
android {
    // ...
    packagingOptions {
        resources {
            excludes += '/META-INF/{AL2.0,LGPL2.1}'
            excludes += '/META-INF/{NOTICE.md,LICENSE.md}' // <-- This line
        }
    }
}

// ...

That resolved it for me, and I'm happy not to have to manually lug around the .jar files anymore: