diff --git a/src/Api/Domain.php b/src/Api/Domain.php
index 0b14684..e05a251 100644
--- a/src/Api/Domain.php
+++ b/src/Api/Domain.php
@@ -90,12 +90,11 @@ class Domain extends HttpApi
 
         if (!empty($smtpPass)) {
             Assert::stringNotEmpty($smtpPass);
-            Assert::lengthBetween($smtpPass, 5, 32, 'SMTP password must be between 5 and 32 characters.');
 
             $params['smtp_password'] = $smtpPass;
         }
 
-        if (null !== $spamAction) {
+        if (!empty($spamAction)) {
             // TODO(sean.johnson): Extended spam filter input validation.
             Assert::stringNotEmpty($spamAction);
 
diff --git a/tests/Api/DomainTest.php b/tests/Api/DomainTest.php
index cbe23ed..86ab5e7 100644
--- a/tests/Api/DomainTest.php
+++ b/tests/Api/DomainTest.php
@@ -85,6 +85,20 @@ JSON
     }
 
     public function testCreateWithPassword()
+    {
+        $this->setRequestMethod('POST');
+        $this->setRequestUri('/v3/domains');
+        $this->setRequestBody([
+            'name' => 'example.com',
+            'smtp_password' => 'foo',
+        ]);
+        $this->setHydrateClass(CreateResponse::class);
+
+        $api = $this->getApiInstance();
+        $api->create('example.com', 'foo');
+    }
+
+    public function testCreateWithPasswordSpamAction()
     {
         $this->setRequestMethod('POST');
         $this->setRequestUri('/v3/domains');
@@ -95,6 +109,22 @@ JSON
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
+        $api = $this->getApiInstance();
+        $api->create('example.com', 'foo', 'bar');
+    }
+
+    public function testCreateWithPasswordSpamActionWildcard()
+    {
+        $this->setRequestMethod('POST');
+        $this->setRequestUri('/v3/domains');
+        $this->setRequestBody([
+            'name' => 'example.com',
+            'smtp_password' => 'foo',
+            'spam_action' => 'bar',
+            'wildcard' => 'true',
+        ]);
+        $this->setHydrateClass(CreateResponse::class);
+
         $api = $this->getApiInstance();
         $api->create('example.com', 'foo', 'bar', true);
     }