diff --git a/test/PHPMailer/PHPMailerTest.php b/test/PHPMailer/PHPMailerTest.php
index 7170b665..845e358c 100644
--- a/test/PHPMailer/PHPMailerTest.php
+++ b/test/PHPMailer/PHPMailerTest.php
@@ -641,29 +641,6 @@ EOT;
         );
     }
 
-    /**
-     * An embedded attachment test with custom cid domain invalid.
-     */
-    public function testEmbeddedImageCustomCidDomainInvalid()
-    {
-        $this->Mail->msgHTML('<!DOCTYPE html>
-<html lang="en">
-  <head>
-    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
-    <title>E-Mail Inline Image Test</title>
-  </head>
-  <body>
-    <p><img src="data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw=="></p>
-  </body>
-</html>', '', false, '@no a valid domain');
-        $this->Mail->preSend();
-        self::assertStringContainsString(
-            'Content-ID: <bb229a48bee31f5d54ca12dc9bd960c6@phpmailer.0>',
-            $this->Mail->getSentMIMEMessage(),
-            'Embedded image header encoding incorrect.'
-        );
-    }
-
     /**
      * An embedded attachment test.
      */
