app/config/config.yml settings:
# Swiftmailer Configuration
swiftmailer:
transport: "%mailer_transport%"
host:      "%mailer_host%"
username:  "%mailer_user%"
password:  "%mailer_password%"
spool:     { type: memory }
port:     587

aap/config/parameters.yml
mailer_transport: smtp
mailer_host: smtp.sendgrid.net
mailer_user: <username>
mailer_password: <password>

$recipient = $this->container->getParameter('contact_email');
$message = Swift_Message::newInstance()
->setFrom($recipient)
->setTo($teenEmailId)
->setSubject('Your order is sent')
->setBody('checking sending email from emailCart');

$result = $this->get('mailer')->send($message, $failures);
$logger->error("email sent to teen ".$result. " fail:".$failures);`

[2018-03-29 06:14:33] app.ERROR: teenemail:skverma_in@yahoo.com --msg:testing only email now --parent email:skvermain@gmail.com sending from:hello@<domain.com> [] []
[2018-03-29 06:14:33] app.ERROR: email sent to teen 1 fail:Array [] []
[2018-03-29 06:14:33] app.ERROR: Email 3 mail sent to Parent:skvermain@gmail.com [] []
[2018-03-29 06:14:33] app.ERROR: Result:1 fail:Array [] []`