I get this error with stock email settings in Laravel 5.1 Homestead when I try to send a password reset mail.
Swift_TransportException in AbstractSmtpTransp
If you don't have access to the .env file, you can add default values to those env calls on app/config/mail.php, like this:
'from' => ['address' => env('MAIL_FROM_EMAIL','do_not_reply@email.com'), 'name' => env('MAIL_FROM_NAME','SpongeBob')],
This approach will try to get the data from the .env file, if there's nothing there, it'll default to whatever you set.