Magento Modules – Fix Issues After Moving from Vendor to Code

you file path must be

app/code/Magentoexplorer/Helloworld/composer.json

{
    "name": "magentoexplorer/helloworld",
    "description": "my module",
    "require": {
        "php": "~5.5.0|~5.6.0|~7.0.0",
        "magento/module-catalog": "101.0.*",
        "magento/module-config": "100.0.*",
        "magento/module-store": "100.0.*",
        "magento/module-customer": "100.1.*",
        "magento/module-backend": "100.0.*",
        "magento/framework": "100.0.*"
    },
    "type": "magento2-module",
    "version": "1.0.0",
    "license": [
        "OSL-3.0",
        "AFL-3.0"
    ],
    "autoload": {
        "files": [
            "registration.php"
        ],
        "psr-4": {
            "Magentoexplorer\\Helloworld\\": ""
        }
    }
}

app/code/Magentoexplorer/Helloworld/registration.php

<?php 
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Magentoexplorer_Helloworld',
    __DIR__
);

now run the cmd php bin/magento setup:upgrade

Let's check the following to make sure it enables.

Checklist:

• Install Mageplaza_Core
• Install correct Magento installation
• Go to correct admin URL
• Flush cache, disable other cache types
• Check it enable: in app/etc/config.php and bin/magento module:status

The Mageplaza SMTP module menu: - Mageplaza > SMTP - Stores > Mageplaza SMTP