How to install? (Manual Mode)
1 - Go to the plugins folder, add a new folder called MauticPostalServerBundle
2 - Reload the plugin list using the command:\
rm -rf var/cache/*
php bin/console mautic:plugins:reload
OR \
Go to /s/plugins and click Install/Upgrade Plugins\
Via composer
composer require lucascosta/postal-server-api-transport-for-mautic