public class Sad extends AppCompatActivity {

        Button button2;
        Button button3;
        final Context context = this;


        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_sad);
        }
        public void onClick (View v) {

            switch (v.getId()) {
                case R.id.button2:
                    Intent h = new Intent(Intent.ACTION_SEND);
                    h.setType("message/rfc822");
                    h.putExtra(Intent.EXTRA_EMAIL  , new String[]{"email"});
                    h.putExtra(Intent.EXTRA_SUBJECT, "Something bothers me");
                    h.putExtra(Intent.EXTRA_TEXT   , "body of email");
                    try {
                        startActivity(Intent.createChooser(h, "Send mail..."));
                    } catch (android.content.ActivityNotFoundException ex) {
                        Toast.makeText(Sad.this, "There are no email clients installed.", Toast.LENGTH_SHORT).show();
                    }
                    break;
                case R.id.button3:

                    BackgroundMail bm = new BackgroundMail(context);
                    bm.setGmailUserName("****@gmail.com");
                    bm.setGmailPassword ("Password");
                    bm.setMailTo("******@gmail.com");
                    bm.setFormSubject("this is the subject");
                    bm.setFormBody("this is the body");
                    bm.send();
            }
            ;
        }}

public class BackgroundMail {
    String TAG = "BackgroundMail";
    private String username;
    private String password;
    private String mailto;
    private String subject;
    private String body;
    private String sendingMessage;
    private String sendingMessageSuccess;
    private String sendingMessageError;
    private boolean processVisibility = true;
    private ArrayList<String> attachments = new ArrayList<>();
    private Context mContext;
    private OnSuccessCallback onSuccessCallback;
    private OnFailCallback onFailCallback;

    public interface OnSuccessCallback {
        void onSuccess();
    }

    public interface OnFailCallback {
        void onFail();
    }

    public BackgroundMail(Fragment fragment) {
        this(fragment.getActivity().getApplicationContext());
    }

    public BackgroundMail(Context context) {
        this.mContext = context;
        this.sendingMessage = context.getString(R.string.msg_sending_email);
        this.sendingMessageSuccess = context.getString(R.string.msg_email_sent_successfully);
        this.sendingMessageError=context.getString(R.string.msg_error_sending_email);
    }

    private BackgroundMail(Builder builder) {
        mContext = builder.context;
        attachments = builder.attachments;
        username = builder.username;
        password = builder.password;
        mailto = builder.mailto;
        subject = builder.subject;
        body = builder.body;
        setSendingMessage(builder.sendingMessage);
        setSendingMessageSuccess(builder.sendingMessageSuccess);
        setSendingMessageError(builder.sendingMessageError);
        processVisibility = builder.processVisibility;
        setOnSuccessCallback(builder.onSuccessCallback);
        setOnFailCallback(builder.onFailCallback);
    }

    public static Builder newBuilder(Context context) {
        return new Builder(context);
    }

    public static Builder newBuilder(Fragment fragment) {
        return new Builder(fragment.getActivity().getApplicationContext());
    }

    public void setGmailUserName(@NonNull String string) {
        this.username = string;
    }

    public void setGmailUserName(@StringRes int strRes) {
        this.username = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getGmailUserName() {
        return username;
    }

    public void setGmailPassword(@NonNull String string) {
        this.password = string;
    }

    public void setGmailPassword(@StringRes int strRes) {
        this.password = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getGmailPassword() {
        return password;
    }

    public void showVisibleProgress(boolean state) {
        this.processVisibility = state;
    }

    public boolean isProgressVisible() {
        return processVisibility;
    }

    public void setMailTo(@NonNull String string) {
        this.mailto = string;
    }

    public void setMailTo(@StringRes int strRes) {
        this.mailto = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getMailTo() {
        return mailto;
    }

    public void setFormSubject(@NonNull String string) {
        this.subject = string;
    }

    public void setFormSubject(@StringRes int strRes) {
        this.subject = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getFormSubject() {
        return subject;
    }

    public void setFormBody(@NonNull String string) {
        this.body = string;
    }

    public void setFormBody(@StringRes int strRes) {
        this.body = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getFormBody() {
        return body;
    }

    public void setSendingMessage(@NonNull String string) {
        this.sendingMessage = string;
    }

    public void setSendingMessage(@StringRes int strRes) {
        this.sendingMessage = mContext.getResources().getString(strRes);
    }

    @NonNull
    public String getSendingMessage() {
        return sendingMessage;
    }

    public void setSendingMessageSuccess(@Nullable String string) {
        this.sendingMessageSuccess = string;
    }

    public void setSendingMessageSuccess(@StringRes int strRes) {
        this.sendingMessageSuccess = mContext.getResources().getString(strRes);
    }

    @Nullable
    public String getSendingMessageSuccess() {
        return sendingMessageSuccess;
    }

    public void setSendingMessageError(@Nullable String string) {
        this.sendingMessageError = string;
    }

    public void setSendingMessageError(@StringRes int strRes) {
        this.sendingMessageError = mContext.getResources().getString(strRes);
    }

    @Nullable
    public String getSeningMessageError() {
        return sendingMessageError;
    }

    public void addAttachment(@NonNull String attachment) {
        this.attachments.add(attachment);
    }

    public void addAttachment(@StringRes int strRes) {
        this.attachments.add(mContext.getResources().getString(strRes));
    }

    public void addAttachments(@NonNull List<String> attachments) {
        this.attachments.addAll(attachments);
    }

    public void addAttachments(String...attachments) {
        this.attachments.addAll(Arrays.asList(attachments));
    }

    @NonNull
    public List<String> getAttachments() {
        return attachments;
    }

    public void setOnSuccessCallback(OnSuccessCallback onSuccessCallback) {
        this.onSuccessCallback = onSuccessCallback;
    }

    public void setOnFailCallback(OnFailCallback onFailCallback) {
        this.onFailCallback = onFailCallback;
    }


    public void send() {

        if (TextUtils.isEmpty(username)) {
            throw new IllegalArgumentException("You didn't set a Gmail username");
        }
        if (TextUtils.isEmpty(password)) {
            throw new IllegalArgumentException("You didn't set a Gmail password");
        }
        if (TextUtils.isEmpty(mailto)) {
            throw new IllegalArgumentException("You didn't set a Gmail recipient");
        }
        if (TextUtils.isEmpty(body)) {
            throw new IllegalArgumentException("You didn't set a body");
        }
        if (TextUtils.isEmpty(subject)) {
            throw new IllegalArgumentException("You didn't set a subject");
        }
        if (!Utils.isNetworkAvailable(mContext)) {
            Log.d(TAG, "you need internet connection to send the email");
        }
        new SendEmailTask().execute();
    }

    public class SendEmailTask extends AsyncTask<String, Void, Boolean> {
        private ProgressDialog progressDialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            if (processVisibility) {
                progressDialog = new ProgressDialog(mContext);
                progressDialog.setMessage(sendingMessage);
                progressDialog.setCancelable(false);
                progressDialog.show();
            }
        }

        @Override
        protected Boolean doInBackground(String... arg0) {
            try {
                GmailSender sender = new GmailSender(username, password);
                if (!attachments.isEmpty()) {
                    for (int i = 0; i < attachments.size(); i++) {
                        if (!attachments.get(i).isEmpty()) {
                            sender.addAttachment(attachments.get(i));
                        }
                    }
                }
                sender.sendMail(subject, body, username, mailto);
            } catch (Exception e) {
                e.printStackTrace();
                return false;
            }
            return true;
        }

        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            if (processVisibility) {
                progressDialog.dismiss();
                if (result) {
                    if (!TextUtils.isEmpty(sendingMessageSuccess)) {
                        Toast.makeText(mContext, sendingMessageSuccess, Toast.LENGTH_SHORT).show();
                    }
                    if (onSuccessCallback != null) {
                        onSuccessCallback.onSuccess();
                    }
                }else {
                    if (!TextUtils.isEmpty(sendingMessageError)) {
                        Toast.makeText(mContext, sendingMessageError, Toast.LENGTH_SHORT).show();
                    }
                    if (onFailCallback != null) {
                        onFailCallback.onFail();
                    }
                }
            }
        }
    }

    public static final class Builder {
        private Context context;
        private String username;
        private String password;
        private String mailto;
        private String subject;
        private String body;
        private ArrayList<String> attachments = new ArrayList<>();
        private String sendingMessage;
        private String sendingMessageSuccess;
        private String sendingMessageError;
        private boolean processVisibility;
        private OnSuccessCallback onSuccessCallback;
        private OnFailCallback onFailCallback;

        private Builder(Context context) {
            this.context = context;
            this.sendingMessage = context.getString(R.string.msg_sending_email);
            this.sendingMessageSuccess = context.getString(R.string.msg_email_sent_successfully);
            this.sendingMessageError=context.getString(R.string.msg_error_sending_email);
        }

        public Builder withUsername(@NonNull String username) {
            this.username = username;
            return this;
        }

        public Builder withUsername(@StringRes int usernameRes) {
            this.username = context.getResources().getString(usernameRes);
            return this;
        }

        public Builder withPassword(@NonNull String password) {
            this.password = password;
            return this;
        }

        public Builder withPassword(@StringRes int passwordRes) {
            this.password = context.getResources().getString(passwordRes);
            return this;
        }

        public Builder withMailto(@NonNull String mailto) {
            this.mailto = mailto;
            return this;
        }

        public Builder withMailto(@StringRes int mailtoRes) {
            this.mailto = context.getResources().getString(mailtoRes);
            return this;
        }

        public Builder withSubject(@NonNull String subject) {
            this.subject = subject;
            return this;
        }

        public Builder withSubject(@StringRes int subjectRes) {
            this.subject = context.getResources().getString(subjectRes);
            return this;
        }

        public Builder withBody(@NonNull String body) {
            this.body = body;
            return this;
        }

        public Builder withBody(@StringRes int bodyRes) {
            this.body = context.getResources().getString(bodyRes);
            return this;
        }

        public Builder withAttachments(@NonNull ArrayList<String> attachments) {
            this.attachments.addAll(attachments);
            return this;
        }

        public Builder withAttachments(String...attachments) {
            this.attachments.addAll(Arrays.asList(attachments));
            return this;
        }

        public Builder withAttachments(@ArrayRes int attachmentsRes) {
            this.attachments.addAll(Arrays.asList(context.getResources().getStringArray(attachmentsRes)));
            return this;
        }

        public Builder withSendingMessage(@NonNull String sendingMessage) {
            this.sendingMessage = sendingMessage;
            return this;
        }

        public Builder withSendingMessage(@StringRes int sendingMessageRes) {
            this.sendingMessage = context.getResources().getString(sendingMessageRes);
            return this;
        }

        public Builder withSendingMessageSuccess(@Nullable String sendingMessageSuccess) {
            this.sendingMessageSuccess = sendingMessageSuccess;
            return this;
        }

        public Builder withSendingMessageSuccess(@StringRes int sendingMessageSuccessRes) {
            this.sendingMessageSuccess = context.getResources().getString(sendingMessageSuccessRes);
            return this;
        }

        public Builder withSendingMessageError(@Nullable String sendingMessageError) {
            this.sendingMessageError = sendingMessageError;
            return this;
        }

        public Builder withSendingMessageError(@StringRes int sendingMessageError) {
            this.sendingMessageError = context.getResources().getString(sendingMessageError);
            return this;
        }

        public Builder withProcessVisibility(boolean processVisibility) {
            this.processVisibility = processVisibility;
            return this;
        }

        public Builder withOnSuccessCallback(OnSuccessCallback onSuccessCallback) {
            this.onSuccessCallback = onSuccessCallback;
            return this;
        }

        public Builder withOnFailCallback(OnFailCallback onFailCallback) {
            this.onFailCallback = onFailCallback;
            return this;
        }

        public BackgroundMail build() {
            return new BackgroundMail(this);
        }

        public BackgroundMail send() {
            BackgroundMail backgroundMail = build();
            backgroundMail.send();
            return backgroundMail;
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="queens.feedback">

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".Happy" />
        <activity android:name=".Sad"></activity>

    </application>

</manifest>

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "22.0.1"

    defaultConfig {
        applicationId "queens.feedback"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 7
        versionName "1.7"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:23.0.0'
}