//config/smtp-settings.php
<?php

return [
    'class' => 'Swift_SmtpTransport',
    'host' => 'humanized.it',
    'encryption' => 'tls', 'port' => '587',
    'streamOptions' => [ 'ssl' =>
        [ 'allow_self_signed' => true,
            'verify_peer' => false,
            'verify_peer_name' => false,
        ],
    ]
];

//config/smtp-settings-aux.php

<?php

return [
    'class' => 'Swift_SmtpTransport',
    'host' => 'humanized.it',
    'encryption' => 'tls', 'port' => '587',
    'streamOptions' => [ 'ssl' =>
        [ 'allow_self_signed' => true,
            'verify_peer' => false,
            'verify_peer_name' => false,
        ],
    ]
];


//config/main.php

Edit components:

    'components' => [
             'mailer' => [
            'class' => 'yii\swiftmailer\Mailer',
            // send all mails to a file by default. You have to set
            // 'useFileTransport' to false and configure a transport
            // for the mailer to send real emails.
            'useFileTransport' => false,
            'transport' => require(__DIR__ . '/smtp-settings(-aux).php'),
        ],