MainActivity.java

 String[] emailContent = {"Hii Abhi!","Here is my new article","abhi@gmail.com"};
        
        Observable.just(emailContent)
                .map(emailData -> {

                    GMailSender sender = new GMailSender("senderemailid@gmail.com",
                            "password");
                    sender.sendMail(emailData[0], emailData[1],
                            "senderemailid",emailData[2]);
                    return "Email Successfully sent";
                    
                })
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeOn(Schedulers.io())
                .subscribe(new DisposableObserver<String>() {
                    @Override
                    public void onNext(String s) {
                        
                        //s wil contain what map() will return
                        Toast.makeText(context, s , Toast.LENGTH_SHORT).show();
                    }

                    @Override
                    public void onError(Throwable e) {
                        Toast.makeText(context,"Email Send failed", Toast.LENGTH_SHORT).show();

                    }

                    @Override
                    public void onComplete() {

                    }
                });