BCC email addresses are ignored

Problem/Motivation

Emails to BCC are never sent.

Steps to reproduce

Set up a webform and add an email handler with a BCC to a email address different to the to. Submit and observe that the bcc email does not get an email address.

Proposed resolution

The problem is that the email is built using:

        return $this->getPreparedHeaders()->toString().$body->toString();

https://git.drupalcode.org/project/amazon_ses/-/blob/3.0.x/src/AmazonSes...

In https://github.com/symfony/symfony/blob/v6.4.41/src/Symfony/Component/Mi...

toString calls

$this->getPreparedHeaders()->toString()

to build the headers in, this explicitly removes the BCC
https://github.com/symfony/symfony/blob/v6.4.41/src/Symfony/Component/Mi...

$headers->remove('Bcc');

Note the above holds in latest symfony/mime - site I found on is still on Drupal 10 hence the links to 6.4.41.

Remaining tasks

User interface changes

API changes

Data model changes