========================================
PRUEBA: SSL implícito  ->  ssl://<smtp_mail_server>:465
========================================
[FALLO] No se pudo conectar: php_network_getaddresses: getaddrinfo failed: Name or service not known (errno 0)

========================================
PRUEBA: STARTTLS  ->  <smtp_mail_server>:587
========================================
[FALLO] No se pudo conectar: php_network_getaddresses: getaddrinfo failed: Name or service not known (errno 0)

========================================
PRUEBA: Plain (sin TLS)  ->  <smtp_mail_server>:25
========================================
[FALLO] No se pudo conectar: php_network_getaddresses: getaddrinfo failed: Name or service not known (errno 0)

Diagnóstico finalizado.