The build failure is unrelated to the changes.

I found some more places. Ready to be reviewed now.

As Address is an immutable object, it should be better to use those as-is instead of creating new instances.

Moreover, we are lacking some escaping to flawlessly use addresses names in email headers.

AFAIK, commas and double quotes have to be escaped.

I use the following code in my project which ATM use the official postmark client:

        $name = preg_replace('/"/u', '\"', $name);
        if (preg_match('/,/u', $name)) {
            $name = sprintf('"%s"', $name);
        }

I quickly looked at RFC, but address grammar can be found in https://tools.ietf.org/html/rfc2822#section-3.4.

I think this one needs to be rebased on 4.3 as this is a bug fix, right? @xabbuh Can you rebase?

Thank you @xabbuh.