That error message means that there was not response OR the server could not be connected.
The following settings worked on my end:
'stream' => [
'ssl' => [
'allow_self_signed' => true,
'verify_peer' => false,
'verify_peer_name' => false,
],
]
Note that my SMTP settings are:
MAIL_DRIVER=smtp
MAIL_HOST=smtp.gmail.com
MAIL_PORT=465
MAIL_USERNAME=[full gmail address]
MAIL_PASSWORD=[App Password obtained after two step verification]
MAIL_ENCRYPTION=ssl