[8.x] Avoid SwiftMailer forceReconnection when not running from a queue daemon

[alim-shapiev]

I have noticed that emails that are sent in bulk all use separate connections (even though they are not simultaneous, there can be a limit of connections per minute per IP set for an SMTP server). As I've found in multiple pull requests (i.e., #4573), there has been a problem with long lasting SMTP connections due to some problems with SwiftMailer and a simple solution for it:

protected function sendSwiftMessage($message)
{
    $this->failedRecipients = [];

    try {
        return $this->swift->send($message, $this->failedRecipients);
    } finally {
        $this->forceReconnection();
    }
}

However, these problems are only encountered when a program is executed from a queue daemon (php artisan queue:work or php artisan queue:listen), so there can be a compromise between dealing with the SSL broken pipe error and sending multiple emails.

I propose setting a flag (or checking somehow else, if there's a better way for it) for when the script is executed from a queue daemon, then, when an email is sent via SMTP and the flag is not present, the SMTP connection will no longer be stopped. This would help in CRON jobs or in case of synchronous mail sending and wouldn't ruin queues a second time.

[alim-shapiev]

As I can see, the tests are failing due to ReflectionException: Class config does not exist.
Is this because the config is not available inside the framework's core somehow?

[driesvints]

We can't use a facade like this here since the mailer component also can act as a standalone component.

[driesvints]

Same here. We can't use a facade here.

[driesvints]

Going to close this one as tests are indeed failing because of the facades. Feel free to re-attempt with a different solution and passing tests 👍