DraftEmail removing bcc from email

We used to have simple mailto: links to provide users a simple way to open a new draft email with the relevant emails directly filled in.

The issue is that there is a limit to the length of href supported by such links (about 2000 chars), and sometimes we'll need more than that.

So to avoid this issue, I'm shifting to a server-side solution by building a new DraftEmail and just send it in my Response after a .toString().

It works fine as long as the emails are provided in the 'to' and 'cc' fields, but the 'bcc' field doesn't work.

It seems to be on purpose :

https://github.com/symfony/symfony/blob/7.3/src/Symfony/Component/Mime/DraftEmail.php

From what I understand, it seems related to the fact that the bcc should not be in the message but in the envelope. Ok, but then what would be a simple way to do what I'm attempting to do? Because as far as I understand, the envelope is used to send the message, but I don't want to send the message, I just want to create it, the sending is handled by the email client.

Another issue is that unlike mailto: links, a DraftEmail doesn't seem to add the signature of the user, I assume it's because it's an external file and not a new message or a reply, but that's an issue as well.

Are there alternatives in symfony to mailto: links that does the same thing as far as signatures and bcc recipients are concerned, while not having the length limitation?

Thank you for your help

Create a custom DraftEmail class that overrides getPreparedHeaders to retain Bcc.

use Symfony\Component\Mime\DraftEmail;
use Symfony\Component\Mime\Header\Headers;

class CustomDraftEmail extends DraftEmail
{
    public function getPreparedHeaders(): Headers
    {
        $headers = clone $this->getHeaders();
        if (!$headers->has('MIME-Version')) {
            $headers->addTextHeader('MIME-Version', '1.0');
        }
        // Do NOT remove Bcc headers
        return $headers;
    }
}

Then use the CustomDraftEmail class to create a draft email and include Bcc recipients in the MIME message.

use App\Mail\CustomDraftEmail;
use Symfony\Component\HttpFoundation\Response;

$email = (new CustomDraftEmail())
    ->to('recipient@example.com')
    ->cc('cc@example.com')
    ->bcc('bcc@example.com')
    ->subject('Test Draft Email')
    ->text('This is the email body.');

$response = new Response($email->toString());
$response->headers->set('Content-Type', 'text/plain'); // Adjust based on delivery method
return $response;

------ Edits
This may be not matching your exact needs but, this is how we fixed the issue.
Like @chris-haas pointed it out, this solution's limitation is a lack of automatic signatures. We mitigated it by appending a placeholder signature to the email body programmatically. (Another alternative can be to Instruct users to add their signature manually after opening the .eml file in their email client):

Create a controller :

use App\Mail\CustomDraftEmail;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\ResponseHeaderBag;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class EmailController extends AbstractController
{
    public function createDraftEmail(): Response
    {
        $email = (new CustomDraftEmail())
            ->to('recipient@example.com')
            ->cc('cc@example.com')
            ->bcc('bcc@example.com')
            ->subject('Test Draft Email')
            ->text("The email body.\n\n-- \nYour Name"); // Here the signature is added

        $response = new Response($email->toString());
        $disposition = $response->headers->makeDisposition(
            ResponseHeaderBag::DISPOSITION_ATTACHMENT,
            'draft-email.eml'
        );
        $response->headers->set('Content-Type', 'message/rfc822');
        $response->headers->set('Content-Disposition', $disposition);

        return $response;
    }
}

When the user clicks a link to this endpoint, their browser will download a .eml file.