check mail encoding and format if charset is not specified

src/MailCollector.php

@@ -2382,6 +2382,19 @@ public function getDecodedContent(Part $part)
         }
 
         $charset = $content_type->getParameter('charset');
+
+        // If charset is not specified, try to detect it automatically
+        if ($charset === null) {
+            // Use mb_detect_encoding to guess the charset
+            $detected_charset = mb_detect_encoding($contents, ['UTF-8', 'ISO-8859-1', 'ISO-8859-15', 'Windows-1252'], true);
+            if ($detected_charset !== false) {
+                $charset = $detected_charset;
+            } else {
+                // Fallback to ISO-8859-1 as it's the most common for mail headers without charset
+                $charset = 'ISO-8859-1';
+            }
+        }
+
         if ($charset !== null && strtoupper($charset) != 'UTF-8') {
             /* mbstring functions do not handle the 'ks_c_5601-1987' &
              * 'ks_c_5601-1989' charsets. However, these charsets are used, for

tests/emails-tests/47-missing-charset.eml

@@ -0,0 +1,25 @@
+From: [email protected]
+To: [email protected]
+Subject: System Report
+MIME-Version: 1.0
+Content-Type: text/plain
+Content-Transfer-Encoding: quoted-printable
+Date: Mon, 21 Oct 2025 10:00:00 +0000
+Message-ID: <[email protected]>
+
+ATTENTION: Ne cliquez pas sur les liens ou n'ouvrez pas les pi=E8ces jointe=
+s si vous n'=EAtes pas s=FBr du contenu.
+
+This is a test message with:
+- Accented characters: =E8 =EA =FB (è ê û in ISO-8859-1)
+- Quote printable encoding
+- NO charset parameter in Content-Type header
+
+The bug is that when charset is missing, these bytes are not converted to UTF-8.
+
+Details:
+=E8 (è), =E9 (é), =EA (ê), =EB (ë)
+=E0 (à), =E2 (â), =E4 (ä)
+=F9 (ù), =FB (û), =FC (ü)
+
+This should be handled correctly by mb_detect_encoding() fallback.

tests/imap/MailCollectorTest.php

@@ -39,6 +39,7 @@
 use ITILFollowup;
 use Laminas\Mail\Protocol\Imap;
 use Laminas\Mail\Protocol\Pop3;
+use Laminas\Mail\Storage\Mbox;
 use Laminas\Mail\Storage\Message;
 use NotificationTarget;
 use NotificationTargetSoftwareLicense;
@@ -1493,4 +1494,24 @@ public function testCleanContent(
         $result = $mailcollector->cleanContent($original);
         $this->assertEquals($expected, $result);
     }
+
+    public function testMissingCharsetMailIsProcessed()
+    {
+        $email_file = GLPI_ROOT . '/tests/emails-tests/47-missing-charset.eml';
+        $this->assertFileExists($email_file);
+
+        $storage = new Mbox(['filename' => $email_file]);
+        $message = $storage->current();
+
+        $body_text = null;
+        foreach ($message as $part) {
+            if ($part->getHeader('content-type')->getType() === 'text/plain') {
+                $body_text = $part->getContent();
+                break;
+            }
+        }
+
+        $this->assertNotNull($body_text, 'No text/plain part found in email');
+        $this->assertStringContainsString('ATTENTION', $body_text);
+    }
 }