How can email sending works (contact- orders - forgot pswd ..) without using a third-party extension ( like Mageplaza_SMTP) ??
Should i make any sort of configuration in my local server ?
Ps : I did all the needed configs in Magento Admin Panel
The server where Magento is installed should have a smtp server installed in order to have email sending working. There is no need for a 3rd party smtp server setup if you have postfix installed... Do you have full control over your server ?