From 04ddc126f3fdf33c2e6da02acf248b5093e6c495 Mon Sep 17 00:00:00 2001
From: ThomasLandauer <thomas@landauer.at>
Date: Mon, 20 Dec 2021 17:37:07 +0100
Subject: [PATCH] [Mime] Relaxing in-reply-to header validation

---
 src/Symfony/Component/Mime/Header/Headers.php      |  4 ++--
 .../Component/Mime/Tests/Header/HeadersTest.php    | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/Symfony/Component/Mime/Header/Headers.php b/src/Symfony/Component/Mime/Header/Headers.php
index 1a7b4b276eee..201a7a5f9744 100644
--- a/src/Symfony/Component/Mime/Header/Headers.php
+++ b/src/Symfony/Component/Mime/Header/Headers.php
@@ -141,8 +141,8 @@ public function add(HeaderInterface $header): self
             'cc' => MailboxListHeader::class,
             'bcc' => MailboxListHeader::class,
             'message-id' => IdentificationHeader::class,
-            'in-reply-to' => IdentificationHeader::class,
-            'references' => IdentificationHeader::class,
+            'in-reply-to' => UnstructuredHeader::class, // `In-Reply-To` and `References` are less strict than RFC 2822 (3.6.4) to allow users entering the original email's ...
+            'references' => UnstructuredHeader::class, // ... `Message-ID`, even if that is no valid `msg-id`
             'return-path' => PathHeader::class,
         ];
 
diff --git a/src/Symfony/Component/Mime/Tests/Header/HeadersTest.php b/src/Symfony/Component/Mime/Tests/Header/HeadersTest.php
index 89d8be01b018..5da27293310e 100644
--- a/src/Symfony/Component/Mime/Tests/Header/HeadersTest.php
+++ b/src/Symfony/Component/Mime/Tests/Header/HeadersTest.php
@@ -243,4 +243,18 @@ public function testToArray()
             "Foo: =?utf-8?Q?aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa?=\r\n =?utf-8?Q?aaaa?=",
         ], $headers->toArray());
     }
+
+    public function testInReplyToAcceptsNonIdentifierValues()
+    {
+        $headers = new Headers();
+        $headers->addHeader('In-Reply-To', 'foobar');
+        $this->assertEquals('foobar', $headers->get('In-Reply-To')->getBody());
+    }
+
+    public function testReferencesAcceptsNonIdentifierValues()
+    {
+        $headers = new Headers();
+        $headers->addHeader('References' , 'foobar');
+        $this->assertEquals('foobar', $headers->get('References')->getBody());
+    }
 }