Symfony version(s) affected: 4.3.x / 4.4

Description

Sending emails with the Mandrill (MailChimp) API doesn't work when using named addresses for recipients or the for sender.

How to reproduce

use Symfony\Component\Mailer\Mailer;
use Symfony\Component\Mime\NamedAddress;
use Symfony\Component\Mailer\Transport;

$transport = Transport::fromDsn(sprintf('api://%s@mandrill', 'YOUR_KEY'));
$mailer = new Mailer($transport);

$email = new Email();
$email
    ->from(new NamedAddress('test@example.com', 'My Name'))
    ->subject('Subject')
    ->text('Message')
    ->to(
        new NamedAddress('recipient@example.com', 'Recipient Name')
    )
;

$mailer->send($email);

The following error will be returned:

Symfony\Component\Mailer\Exception\TransportException: Unable to send an email: Validation error: {"message":{"from_email":"The username portion of the email address is invalid (the portion before the @: My Name (code -2). in /var/www/html/wp-content/plugins/wmach/vendor/symfony/mailchimp-mailer/Http/Api/MandrillTransport.php:48

Possible Solution

The My Name <test@example.com> encoding of email addressed should not be used for Mandrill API. Specific parameters (from_name for sender, name for recipients) should be used instead (see API documentation).

Additional context