Need help: Copy a message sent via SMTP to "Sent" folder by IMAP about php-imap

[PhilippGrashoff]

The solution is utterly simple. My misconception was that a Message object was needed for this - it isn't.
Here is a working solution:

           ...
           $client = $this->createImapClient();
           $client->connection->appendMessage(
                $this->emailAccount->get('imap_sent_folder'),
                $this->getSentMIMEMessage()
            );
            ...

    protected function createImapClient(): Client
    {
        $cm = new ClientManager();
        $client = $cm->make(
            [
                'host' => $this->emailAccount->get('imap_host'),
                'port' => $this->emailAccount->get('imap_port'),
                'encryption' => $this->emailAccount->get('imap_port') == 993 ? 'ssl' : 'starttls',
                'validate_cert' => true,
                'username' => $this->emailAccount->get('user'),
                'password' => $this->emailAccount->get('password'),
                'protocol' => 'imap'
            ]
        );

        $client->connect();

        return $client;
    }