bug #36947 [Mime] Allow email message to have "To", "Cc", or "Bcc" he…

…ader to be valid (Ernest Hymel)

This PR was submitted for the master branch but it was merged into the 4.4 branch instead.

Discussion
----------

[Mime] Allow email message to have "To", "Cc", or "Bcc" header to be valid

| Q             | A
| ------------- | ---
| Branch?       | 5.0
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #36944
| License       | MIT
| Doc PR        | N/A

Allow emails to have any one of To:, Cc:, or Bcc: fields rather than forcing a required To: field.

Commits
-------

35b7e1c Allow email message to have "To", "Cc", or "Bcc" header to be valid

src/Symfony/Component/Mime/Message.php

@@ -122,8 +122,8 @@ public function toIterable(): iterable
 
     public function ensureValidity()
     {
-        if (!$this->headers->has('To')) {
-            throw new LogicException('An email must have a "To" header.');
+        if (!$this->headers->has('To') && !$this->headers->has('Cc') && !$this->headers->has('Bcc')) {
+            throw new LogicException('An email must have a "To", "Cc", or "Bcc" header.');
         }
 
         if (!$this->headers->has('From') && !$this->headers->has('Sender')) {