diff --git a/.gitignore b/.gitignore
index 5f49d65d5..18da1fe05 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,7 +20,6 @@
 /issues
 .idea/
 .env
-/test
 /public_html
 /vendors/knockout/spec
 /vendors/openpgp-5
diff --git a/snappymail/v/0.0.0/app/libraries/snappymail/smime/openssl.php b/snappymail/v/0.0.0/app/libraries/snappymail/smime/openssl.php
index 3af3b7f25..c7bc0c059 100644
--- a/snappymail/v/0.0.0/app/libraries/snappymail/smime/openssl.php
+++ b/snappymail/v/0.0.0/app/libraries/snappymail/smime/openssl.php
@@ -324,10 +324,11 @@ class OpenSSL
 			$opaque |= \str_contains($input, 'application/pkcs7-mime') || \str_contains($input, 'application/x-pkcs7-mime');
 			$input = $tmp;
 		}
+		// First pass extracts the content and nothing else: PKCS7_NOSIGS skips the
+		// signature check, so a message with a broken signature can still be read.
 		$output = $opaque ? new Temporary('smimeout-') : null;
 		if (true !== \openssl_pkcs7_verify(
 			$input->filename(),
-//			$flags = 0, // \PKCS7_NOVERIFY | \PKCS7_NOCHAIN | \PKCS7_NOSIGS
 			\PKCS7_NOVERIFY | \PKCS7_NOCHAIN | \PKCS7_NOSIGS,
 			$signers_certificates_filename ?: null,
 			$ca_info = [],
@@ -337,9 +338,23 @@ class OpenSSL
 		)) {
 			throw new \RuntimeException('OpenSSL verify: ' . \openssl_error_string());
 		}
+		// Second pass is the verdict. It used to be the first pass returning true,
+		// which with PKCS7_NOSIGS it does for any well-formed message, so altered
+		// or forged content was reported as validly signed. This checks the
+		// signature against the signer certificate in the message. PKCS7_NOVERIFY
+		// stays: the signer's chain is not checked against any CA, so 'success'
+		// means the content is what the certificate holder signed, not that the
+		// certificate itself is trusted.
+		$verified = \openssl_pkcs7_verify(
+			$input->filename(),
+			\PKCS7_NOVERIFY,
+			null,
+			[],
+			$this->untrusted_certificates_filename
+		);
 		return [
 			'body' => $output ? $output->getContents() : null,
-			'success' => true
+			'success' => true === $verified
 		];
 	}
 }
diff --git a/test/smime-verify.php b/test/smime-verify.php
new file mode 100644
index 000000000..8529b14d2
--- /dev/null
+++ b/test/smime-verify.php
@@ -0,0 +1,69 @@
+<?php
+
+// Run with: php test/smime-verify.php
+spl_autoload_register(static function (string $class): void {
+	$base = dirname(__DIR__).'/tachyon/v/0.0.0/app/libraries/';
+	$file = str_starts_with($class, 'Tachyon\\Util\\')
+		? $base.'tachyon_util/'.strtolower(str_replace('\\', '/', substr($class, 13))).'.php'
+		: $base.str_replace('\\', '/', $class).'.php';
+	if (is_file($file)) {
+		require_once $file;
+	}
+});
+
+function check(bool $condition, string $message): void
+{
+	if (!$condition) {
+		throw new RuntimeException($message);
+	}
+}
+
+$dir = sys_get_temp_dir().'/smime-verify-test-'.getmypid();
+mkdir($dir);
+$key = openssl_pkey_new(['private_key_bits' => 2048, 'private_key_type' => OPENSSL_KEYTYPE_RSA]);
+$cert = openssl_csr_sign(openssl_csr_new(['commonName' => 'signer@example.com'], $key), null, $key, 1);
+openssl_x509_export_to_file($cert, "{$dir}/cert.pem");
+openssl_pkey_export_to_file($key, "{$dir}/key.pem");
+
+$content = "Content-Type: text/plain\r\n\r\nPay 100 EUR to account A.\r\n";
+file_put_contents("{$dir}/in.txt", $content);
+
+$smime = new \Tachyon\Util\SMime\OpenSSL($dir);
+
+// Detached (multipart/signed) and opaque (application/pkcs7-mime) signatures.
+foreach (['detached' => PKCS7_DETACHED, 'opaque' => 0] as $kind => $flags) {
+	check(openssl_pkcs7_sign("{$dir}/in.txt", "{$dir}/signed.eml", "file://{$dir}/cert.pem", "file://{$dir}/key.pem", [], $flags),
+		"{$kind}: signing failed: ".openssl_error_string());
+	$signed = file_get_contents("{$dir}/signed.eml");
+	$opaque = 'opaque' === $kind;
+
+	$result = $smime->verify($signed, null, $opaque);
+	check(true === $result['success'], "{$kind}: intact message not reported as validly signed");
+	if ($opaque) {
+		check(str_contains($result['body'], 'Pay 100 EUR to account A.'), "{$kind}: content not extracted");
+	}
+
+	// Alter the signed content. Detached: the clear text part. Opaque: a byte of
+	// the base64 payload, chosen inside the encapsulated content.
+	if ($opaque) {
+		[$head, $b64] = explode("\n\n", str_replace("\r\n", "\n", $signed), 2);
+		$der = base64_decode($b64);
+		$pos = strpos($der, 'account A');
+		check(false !== $pos, "{$kind}: test could not find the content to alter");
+		$der[$pos + 8] = 'B';
+		$tampered = $head."\n\n".chunk_split(base64_encode($der), 64, "\n");
+	} else {
+		$tampered = str_replace('account A', 'account B', $signed);
+	}
+	check($tampered !== $signed, "{$kind}: test failed to alter the message");
+
+	$result = $smime->verify($tampered, null, $opaque);
+	check(false === $result['success'], "{$kind}: ALTERED message reported as validly signed");
+	if ($opaque) {
+		check(str_contains($result['body'], 'account B'), "{$kind}: altered content no longer readable");
+	}
+}
+
+array_map('unlink', glob("{$dir}/*"));
+rmdir($dir);
+echo "smime-verify: ok\n";