这个方法对我有用。它打开Gmail应用程序(如果安装)，并设置邮件。

public void openGmail(Activity activity) {
    Intent emailIntent = new Intent(Intent.ACTION_VIEW);
    emailIntent.setType("text/plain");
    emailIntent.setType("message/rfc822");
    emailIntent.setData(Uri.parse("mailto:"+activity.getString(R.string.mail_to)));
    emailIntent.putExtra(Intent.EXTRA_SUBJECT, activity.getString(R.string.app_name) + " - info ");
    final PackageManager pm = activity.getPackageManager();
    final List<ResolveInfo> matches = pm.queryIntentActivities(emailIntent, 0);
    ResolveInfo best = null;
    for (final ResolveInfo info : matches)
        if (info.activityInfo.packageName.endsWith(".gm") || info.activityInfo.name.toLowerCase().contains("gmail"))
            best = info;
    if (best != null)
        emailIntent.setClassName(best.activityInfo.packageName, best.activityInfo.name);
    activity.startActivity(emailIntent);
}

最好的(也是最简单的)方法是使用Intent:

Intent i = new Intent(Intent.ACTION_SEND);
i.setType("message/rfc822");
i.putExtra(Intent.EXTRA_EMAIL  , new String[]{"recipient@example.com"});
i.putExtra(Intent.EXTRA_SUBJECT, "subject of email");
i.putExtra(Intent.EXTRA_TEXT   , "body of email");
try {
    startActivity(Intent.createChooser(i, "Send mail..."));
} catch (android.content.ActivityNotFoundException ex) {
    Toast.makeText(MyActivity.this, "There are no email clients installed.", Toast.LENGTH_SHORT).show();
}

否则你就得自己写客户端了。

发送电子邮件可以用intent完成，不需要配置。但这样就需要用户交互，布局也会受到一些限制。

在没有用户交互的情况下构建和发送更复杂的电子邮件需要构建自己的客户端。第一件事是用于电子邮件的Sun Java API不可用。我曾经成功地利用Apache Mime4j库来构建电子邮件。都是基于nilvec的文件。

/**
 * Will start the chosen Email app
 *
 * @param context    current component context.
 * @param emails     Emails you would like to send to.
 * @param subject    The subject that will be used in the Email app.
 * @param forceGmail True - if you want to open Gmail app, False otherwise. If the Gmail
 *                   app is not installed on this device a chooser will be shown.
 */
public static void sendEmail(Context context, String[] emails, String subject, boolean forceGmail) {

    Intent i = new Intent(Intent.ACTION_SENDTO);
    i.setData(Uri.parse("mailto:"));
    i.putExtra(Intent.EXTRA_EMAIL, emails);
    i.putExtra(Intent.EXTRA_SUBJECT, subject);
    if (forceGmail && isPackageInstalled(context, "com.google.android.gm")) {
        i.setPackage("com.google.android.gm");
        i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(i);
    } else {
        try {
            context.startActivity(Intent.createChooser(i, "Send mail..."));
        } catch (ActivityNotFoundException e) {
            Toast.makeText(context, "No email app is installed on your device...", Toast.LENGTH_SHORT).show();
        }
    }
}

/**
 * Check if the given app is installed on this devuice.
 *
 * @param context     current component context.
 * @param packageName The package name you would like to check.
 * @return True if this package exist, otherwise False.
 */
public static boolean isPackageInstalled(@NonNull Context context, @NonNull String packageName) {
    PackageManager pm = context.getPackageManager();
    if (pm != null) {
        try {
            pm.getPackageInfo(packageName, 0);
            return true;
        } catch (PackageManager.NameNotFoundException e) {
            e.printStackTrace();
        }
    }
    return false;
}

这是在Android上发送电子邮件最简洁的方式。

 val intent = Intent(Intent.ACTION_SENDTO).apply {
    data = Uri.parse("mailto:")
    putExtra(Intent.EXTRA_EMAIL, arrayOf("email@example.com"))
    putExtra(Intent.EXTRA_SUBJECT, "Subject")
    putExtra(Intent.EXTRA_TEXT, "Email body")
}
if (intent.resolveActivity(packageManager) != null) {
    startActivity(intent)
}

您还需要在清单中(在应用程序标记之外)指定处理电子邮件的应用程序的查询(mailto)。

<queries>
    <intent>
        <action android:name="android.intent.action.SENDTO" />
        <data android:scheme="mailto" />
    </intent>
</queries>

如果你需要在电子邮件正文中发送HTML文本，请将“电子邮件正文”替换为你的电子邮件字符串，就像这样(请注意HTML . fromhtml可能已经弃用了，这只是为了告诉你如何做)

Html.fromHtml(
    StringBuilder().append("<b>Hello world</b>").toString()
)

使用. settype ("message/rfc822")或ACTION_SEND的策略似乎也适用于非电子邮件客户端的应用程序，如Android Beam和蓝牙。

使用ACTION_SENDTO和mailto: URI似乎工作得很好，并且在开发人员文档中推荐使用。但是，如果你在官方模拟器上这样做，并且没有设置任何电子邮件帐户(或者没有任何邮件客户端)，你会得到以下错误:

不支持的操作 目前不支持该操作。

如下图所示:

结果是模拟器将意图解析为一个名为com.android.fallback的活动。Fallback，它显示上面的消息。显然这是故意的。

如果你想让你的应用在官方模拟器上也能正常运行，你可以在发送邮件之前检查一下:

private void sendEmail() {
    Intent intent = new Intent(Intent.ACTION_SENDTO)
        .setData(new Uri.Builder().scheme("mailto").build())
        .putExtra(Intent.EXTRA_EMAIL, new String[]{ "John Smith <johnsmith@yourdomain.com>" })
        .putExtra(Intent.EXTRA_SUBJECT, "Email subject")
        .putExtra(Intent.EXTRA_TEXT, "Email body")
    ;

    ComponentName emailApp = intent.resolveActivity(getPackageManager());
    ComponentName unsupportedAction = ComponentName.unflattenFromString("com.android.fallback/.Fallback");
    if (emailApp != null && !emailApp.equals(unsupportedAction))
        try {
            // Needed to customise the chooser dialog title since it might default to "Share with"
            // Note that the chooser will still be skipped if only one app is matched
            Intent chooser = Intent.createChooser(intent, "Send email with");
            startActivity(chooser);
            return;
        }
        catch (ActivityNotFoundException ignored) {
        }

    Toast
        .makeText(this, "Couldn't find an email app and account", Toast.LENGTH_LONG)
        .show();
}

在开发人员文档中找到更多信息。