diff --git a/src/applications/config/check/PhabricatorMailSetupCheck.php b/src/applications/config/check/PhabricatorMailSetupCheck.php
index 2b8e4e12d5..b3b6143ad0 100644
--- a/src/applications/config/check/PhabricatorMailSetupCheck.php
+++ b/src/applications/config/check/PhabricatorMailSetupCheck.php
@@ -1,100 +1,104 @@
 <?php
 
 final class PhabricatorMailSetupCheck extends PhabricatorSetupCheck {
 
   public function getDefaultGroup() {
     return self::GROUP_OTHER;
   }
 
   protected function executeChecks() {
+    if (PhabricatorEnv::getEnvConfig('cluster.mailers')) {
+      return;
+    }
+
     $adapter = PhabricatorEnv::getEnvConfig('metamta.mail-adapter');
 
     switch ($adapter) {
       case 'PhabricatorMailImplementationPHPMailerLiteAdapter':
         if (!Filesystem::pathExists('/usr/bin/sendmail') &&
             !Filesystem::pathExists('/usr/sbin/sendmail')) {
           $message = pht(
             'Mail is configured to send via sendmail, but this system has '.
             'no sendmail binary. Install sendmail or choose a different '.
             'mail adapter.');
 
           $this->newIssue('config.metamta.mail-adapter')
             ->setShortName(pht('Missing Sendmail'))
             ->setName(pht('No Sendmail Binary Found'))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter');
         }
         break;
       case 'PhabricatorMailImplementationAmazonSESAdapter':
         if (PhabricatorEnv::getEnvConfig('metamta.can-send-as-user')) {
           $message = pht(
             'Amazon SES does not support sending email as users. Disable '.
             'send as user, or choose a different mail adapter.');
 
           $this->newIssue('config.can-send-as-user')
             ->setName(pht("SES Can't Send As User"))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter')
             ->addPhabricatorConfig('metamta.can-send-as-user');
         }
 
         if (!PhabricatorEnv::getEnvConfig('amazon-ses.access-key')) {
           $message = pht(
             'Amazon SES is selected as the mail adapter, but no SES access '.
             'key is configured. Provide an SES access key, or choose a '.
             'different mail adapter.');
 
           $this->newIssue('config.amazon-ses.access-key')
             ->setName(pht('Amazon SES Access Key Not Set'))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter')
             ->addPhabricatorConfig('amazon-ses.access-key');
         }
 
         if (!PhabricatorEnv::getEnvConfig('amazon-ses.secret-key')) {
           $message = pht(
             'Amazon SES is selected as the mail adapter, but no SES secret '.
             'key is configured. Provide an SES secret key, or choose a '.
             'different mail adapter.');
 
           $this->newIssue('config.amazon-ses.secret-key')
             ->setName(pht('Amazon SES Secret Key Not Set'))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter')
             ->addPhabricatorConfig('amazon-ses.secret-key');
         }
 
         if (!PhabricatorEnv::getEnvConfig('amazon-ses.endpoint')) {
           $message = pht(
             'Amazon SES is selected as the mail adapter, but no SES endpoint '.
             'is configured. Provide an SES endpoint or choose a different '.
             'mail adapter.');
 
           $this->newIssue('config.amazon-ses.endpoint')
             ->setName(pht('Amazon SES Endpoint Not Set'))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter')
             ->addPhabricatorConfig('amazon-ses.endpoint');
         }
 
         $address_key = 'metamta.default-address';
         $options = PhabricatorApplicationConfigOptions::loadAllOptions();
         $default = $options[$address_key]->getDefault();
         $value = PhabricatorEnv::getEnvConfig($address_key);
         if ($default === $value) {
           $message = pht(
             'Amazon SES requires verification of the "From" address, but '.
             'you have not configured a "From" address. Configure and verify '.
             'a "From" address, or choose a different mail adapter.');
 
           $this->newIssue('config.metamta.default-address')
             ->setName(pht('No SES From Address Configured'))
             ->setMessage($message)
             ->addRelatedPhabricatorConfig('metamta.mail-adapter')
             ->addPhabricatorConfig('metamta.default-address');
         }
         break;
     }
 
   }
 }
diff --git a/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php b/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
index 2a7550c419..b3b110298f 100644
--- a/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
+++ b/src/infrastructure/cluster/config/PhabricatorClusterMailersConfigType.php
@@ -1,100 +1,100 @@
 <?php
 
 final class PhabricatorClusterMailersConfigType
   extends PhabricatorJSONConfigType {
 
   const TYPEKEY = 'cluster.mailers';
 
   public function validateStoredValue(
     PhabricatorConfigOption $option,
     $value) {
 
     if ($value === null) {
       return;
     }
 
     if (!is_array($value)) {
       throw $this->newException(
         pht(
           'Mailer cluster configuration is not valid: it should be a list '.
           'of mailer configurations.'));
     }
 
     foreach ($value as $index => $spec) {
       if (!is_array($spec)) {
         throw $this->newException(
           pht(
             'Mailer cluster configuration is not valid: each entry in the '.
             'list must be a dictionary describing a mailer, but the value '.
             'with index "%s" is not a dictionary.',
             $index));
       }
     }
 
     $adapters = PhabricatorMailImplementationAdapter::getAllAdapters();
 
     $map = array();
     foreach ($value as $index => $spec) {
       try {
         PhutilTypeSpec::checkMap(
           $spec,
           array(
             'key' => 'string',
             'type' => 'string',
             'priority' => 'optional int',
             'options' => 'optional wild',
           ));
       } catch (Exception $ex) {
         throw $this->newException(
           pht(
             'Mailer configuration has an invalid mailer specification '.
             '(at index "%s"): %s.',
             $index,
             $ex->getMessage()));
       }
 
       $key = $spec['key'];
       if (isset($map[$key])) {
         throw $this->newException(
           pht(
             'Mailer configuration is invalid: multiple mailers have the same '.
             'key ("%s"). Each mailer must have a unique key.',
             $key));
       }
       $map[$key] = true;
 
-      $priority = idx($spec, 'priority', 0);
-      if ($priority <= 0) {
+      $priority = idx($spec, 'priority');
+      if ($priority !== null && $priority <= 0) {
         throw $this->newException(
           pht(
             'Mailer configuration ("%s") is invalid: priority must be '.
             'greater than 0.',
             $key));
       }
 
       $type = $spec['type'];
       if (!isset($adapters[$type])) {
         throw $this->newException(
           pht(
             'Mailer configuration ("%s") is invalid: mailer type ("%s") is '.
             'unknown. Supported mailer types are: %s.',
             $key,
             $type,
             implode(', ', array_keys($adapters))));
       }
 
       $options = idx($spec, 'options', array());
       try {
         id(clone $adapters[$type])->validateOptions($options);
       } catch (Exception $ex) {
         throw $this->newException(
           pht(
             'Mailer configuration ("%s") specifies invalid options for '.
             'mailer: %s',
             $key,
             $ex->getMessage()));
       }
     }
   }
 
 }