diff --git a/.gitignore b/.gitignore
index 989164d65..d3c6c62fd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 docs/phpdoc/
 test/message.txt
 test/testbootstrap.php
+test/*.pem
 .idea
 build/
diff --git a/class.phpmailer.php b/class.phpmailer.php
index 1faaabd43..e45b3070a 100644
--- a/class.phpmailer.php
+++ b/class.phpmailer.php
@@ -536,6 +536,13 @@ class PHPMailer
      */
     protected $sign_key_file = '';
 
+    /**
+     * The optional S/MIME extra certificates ("CA Chain") file path.
+     * @type string
+     * @access protected
+     */
+    protected $sign_extracerts_file = '';
+
     /**
      * The S/MIME password for the key.
      * Used only if the key is encrypted.
@@ -1971,7 +1978,9 @@ public function createBody()
                     $signed,
                     'file://' . realpath($this->sign_cert_file),
                     array('file://' . realpath($this->sign_key_file), $this->sign_key_pass),
-                    null
+                    null,
+                    PKCS7_DETACHED,
+                    $this->sign_extracerts_file
                 )
                 ) {
                     @unlink($file);
@@ -3244,12 +3253,14 @@ public static function normalizeBreaks($text, $breaktype = "\r\n")
      * @param string $cert_filename
      * @param string $key_filename
      * @param string $key_pass Password for private key
+     * @param string $extracerts_filename Optional path to chain certificate
      */
-    public function sign($cert_filename, $key_filename, $key_pass)
+    public function sign($cert_filename, $key_filename, $key_pass, $extracerts_filename = '')
     {
         $this->sign_cert_file = $cert_filename;
         $this->sign_key_file = $key_filename;
         $this->sign_key_pass = $key_pass;
+        $this->sign_extracerts_file = $extracerts_filename;
     }
 
     /**
diff --git a/test/phpmailerTest.php b/test/phpmailerTest.php
index 2fd66e6eb..b59a89497 100644
--- a/test/phpmailerTest.php
+++ b/test/phpmailerTest.php
@@ -1260,7 +1260,7 @@ public function testBase64()
         $this->assertTrue($this->Mail->send(), 'Base64 encoding failed');
     }
     /**
-     * S/MIME Signing tests.
+     * S/MIME Signing tests (self-signed).
      */
     public function testSigning()
     {
@@ -1277,12 +1277,17 @@ public function testSigning()
             'commonName' => 'PHPMailer Test',
             'emailAddress' => 'phpmailer@example.com'
         );
+        $keyconfig = array(
+            "digest_alg" => "sha256",
+            "private_key_bits" => 2048,
+            "private_key_type" => OPENSSL_KEYTYPE_RSA,
+        );
         $password = 'password';
         $certfile = 'certfile.txt';
         $keyfile = 'keyfile.txt';
 
         //Make a new key pair
-        $pk = openssl_pkey_new();
+        $pk = openssl_pkey_new($keyconfig);
         //Create a certificate signing request
         $csr = openssl_csr_new($dn, $pk);
         //Create a self-signed cert
@@ -1304,6 +1309,88 @@ public function testSigning()
         unlink($keyfile);
     }
 
+    /**
+     * S/MIME Signing tests using a CA chain cert.
+     * To test that a generated message is signed correctly, save the message in a file
+     * and use openssl along with the certs generated by this script:
+     * `openssl smime -verify -in signed.eml -signer certfile.pem -CAfile cacertfile.pem`
+     */
+    public function testSigningWithCA()
+    {
+        $this->Mail->Subject .= ': S/MIME signing with CA';
+        $this->Mail->Body = 'This message is S/MIME signed with an extra CA cert.';
+        $this->buildBody();
+
+        $certprops = array(
+            'countryName' => 'UK',
+            'stateOrProvinceName' => 'Here',
+            'localityName' => 'There',
+            'organizationName' => 'PHP',
+            'organizationalUnitName' => 'PHPMailer',
+            'commonName' => 'PHPMailer Test',
+            'emailAddress' => 'phpmailer@example.com'
+        );
+        $cacertprops = array(
+            'countryName' => 'UK',
+            'stateOrProvinceName' => 'Here',
+            'localityName' => 'There',
+            'organizationName' => 'PHP',
+            'organizationalUnitName' => 'PHPMailer CA',
+            'commonName' => 'PHPMailer Test CA',
+            'emailAddress' => 'phpmailer@example.com'
+        );
+        $keyconfig = array(
+            "digest_alg" => "sha256",
+            "private_key_bits" => 2048,
+            "private_key_type" => OPENSSL_KEYTYPE_RSA,
+        );
+        $password = 'password';
+        $cacertfile = 'cacertfile.pem';
+        $cakeyfile = 'cakeyfile.pem';
+        $certfile = 'certfile.pem';
+        $keyfile = 'keyfile.pem';
+
+        //Create a CA cert
+        //Make a new key pair
+        $capk = openssl_pkey_new($keyconfig);
+        //Create a certificate signing request
+        $csr = openssl_csr_new($cacertprops, $capk);
+        //Create a self-signed cert
+        $cert = openssl_csr_sign($csr, null, $capk, 1);
+        //Save the CA cert
+        openssl_x509_export($cert, $certout);
+        file_put_contents($cacertfile, $certout);
+        //Save the CA key
+        openssl_pkey_export($capk, $pkeyout, $password);
+        file_put_contents($cakeyfile, $pkeyout);
+
+        //Create a cert signed by our CA
+        //Make a new key pair
+        $pk = openssl_pkey_new($keyconfig);
+        //Create a certificate signing request
+        $csr = openssl_csr_new($certprops, $pk);
+        //Create a self-signed cert
+        $cert = openssl_csr_sign($csr, 'file://' . $cacertfile, $capk, 1);
+        //Save the cert
+        openssl_x509_export($cert, $certout);
+        file_put_contents($certfile, $certout);
+        //Save the key
+        openssl_pkey_export($pk, $pkeyout, $password);
+        file_put_contents($keyfile, $pkeyout);
+
+        $this->Mail->sign(
+            $certfile,
+            $keyfile,
+            $password,
+            $cacertfile
+        );
+        $this->assertTrue($this->Mail->send(), 'S/MIME signing with CA failed');
+        unlink($cacertfile);
+        unlink($cakeyfile);
+        unlink($certfile);
+        unlink($keyfile);
+    }
+
     /**
      * DKIM Signing tests.
      */