AssertionError for legacy email with lower-case address headers

Thanks for the report. I believe it is confusion over the header case (as a workaround, probably 'Bcc' would work). Probably introduced by #3334230: Support all headers in LegacyEmailBuilder, where the different cases were starting to drive me crazy😃.

The simplest fix is to change LegacyMailerHelper::emailFromArray() where the comment says "Convert to standard case.", make it like this

        // Convert to standard case.
        $name = ucfirst($name))
        if ($name == 'Reply-to') {
          $name = 'Reply-To';
        }

Another option is to copy what Symfony library code does and store all headers in lower case internally. We need to be careful with legacy emails though as Drupal uses capitals.

Thanks for reporting back.

Faced the same issue when upgrading to Drupal 10. The tests will fail without the $name = ucfirst($name)) change.

Thanks for the patch. It's good and it works.

Two comments please:

1. Symfony library stores all headers in lower case. I think the patch would be even better if we do the same. It's consistent with the library, and simpler code. We can remove if ($name == 'Reply-to') and we don't need to call ucfirst().
2. There is a similar problem on BaseEmailTrait::setAddress() - we can put $name = strtolower($name) there too. Then fix all the string constants to lower case 'from' instead of 'From' etc.

I hope I got all changes requested.

Missed a one thing on my previous patch.

Great thanks.

public function setAddress(string $name, $addresses) {
     assert(isset($this->addresses[$name]));
-    if ($name == 'To') {
+    $name = strtolower($name);
+    if ($name == 'to') {
       $this->valid(self::PHASE_BUILD);
     }

You should put the strtolower before the assert.

Then you can put ToEmailAdjuster back as it was or also change the other 4 for consistency.

Updated the all adjuster constants to lowercase.

Great thanks