Remove all legacy configuration options for mailers

Summary:
Ref T920. About a year ago (in 2018 Week 6, see D19003) we moved from individually configured mailers to `cluster.mailers`, primarily to support fallback across multiple mail providers.

Since this has been stable for quite a while, drop support for the older options.

Test Plan: Grepped for all removed options.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T920

Differential Revision: https://secure.phabricator.com/D19940

src/__phutil_library_map__.php

@@ -3405,10 +3405,8 @@ phutil_register_library_map(array(
     'PhabricatorMailReceiverTestCase' => 'applications/metamta/receiver/__tests__/PhabricatorMailReceiverTestCase.php',
     'PhabricatorMailReplyHandler' => 'applications/metamta/replyhandler/PhabricatorMailReplyHandler.php',
     'PhabricatorMailRoutingRule' => 'applications/metamta/constants/PhabricatorMailRoutingRule.php',
-    'PhabricatorMailSetupCheck' => 'applications/config/check/PhabricatorMailSetupCheck.php',
     'PhabricatorMailStamp' => 'applications/metamta/stamp/PhabricatorMailStamp.php',
     'PhabricatorMailTarget' => 'applications/metamta/replyhandler/PhabricatorMailTarget.php',
-    'PhabricatorMailgunConfigOptions' => 'applications/config/option/PhabricatorMailgunConfigOptions.php',
     'PhabricatorMainMenuBarExtension' => 'view/page/menu/PhabricatorMainMenuBarExtension.php',
     'PhabricatorMainMenuSearchView' => 'view/page/menu/PhabricatorMainMenuSearchView.php',
     'PhabricatorMainMenuView' => 'view/page/menu/PhabricatorMainMenuView.php',
@@ -3657,7 +3655,6 @@ phutil_register_library_map(array(
     'PhabricatorPHIDsSearchField' => 'applications/search/field/PhabricatorPHIDsSearchField.php',
     'PhabricatorPHPASTApplication' => 'applications/phpast/application/PhabricatorPHPASTApplication.php',
     'PhabricatorPHPConfigSetupCheck' => 'applications/config/check/PhabricatorPHPConfigSetupCheck.php',
-    'PhabricatorPHPMailerConfigOptions' => 'applications/config/option/PhabricatorPHPMailerConfigOptions.php',
     'PhabricatorPHPPreflightSetupCheck' => 'applications/config/check/PhabricatorPHPPreflightSetupCheck.php',
     'PhabricatorPackagesApplication' => 'applications/packages/application/PhabricatorPackagesApplication.php',
     'PhabricatorPackagesController' => 'applications/packages/controller/PhabricatorPackagesController.php',
@@ -4312,7 +4309,6 @@ phutil_register_library_map(array(
     'PhabricatorSecuritySetupCheck' => 'applications/config/check/PhabricatorSecuritySetupCheck.php',
     'PhabricatorSelectEditField' => 'applications/transactions/editfield/PhabricatorSelectEditField.php',
     'PhabricatorSelectSetting' => 'applications/settings/setting/PhabricatorSelectSetting.php',
-    'PhabricatorSendGridConfigOptions' => 'applications/config/option/PhabricatorSendGridConfigOptions.php',
     'PhabricatorSessionsSettingsPanel' => 'applications/settings/panel/PhabricatorSessionsSettingsPanel.php',
     'PhabricatorSetConfigType' => 'applications/config/type/PhabricatorSetConfigType.php',
     'PhabricatorSetting' => 'applications/settings/setting/PhabricatorSetting.php',
@@ -9214,10 +9210,8 @@ phutil_register_library_map(array(
     'PhabricatorMailReceiverTestCase' => 'PhabricatorTestCase',
     'PhabricatorMailReplyHandler' => 'Phobject',
     'PhabricatorMailRoutingRule' => 'Phobject',
-    'PhabricatorMailSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorMailStamp' => 'Phobject',
     'PhabricatorMailTarget' => 'Phobject',
-    'PhabricatorMailgunConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorMainMenuBarExtension' => 'Phobject',
     'PhabricatorMainMenuSearchView' => 'AphrontView',
     'PhabricatorMainMenuView' => 'AphrontView',
@@ -9509,7 +9503,6 @@ phutil_register_library_map(array(
     'PhabricatorPHIDsSearchField' => 'PhabricatorSearchField',
     'PhabricatorPHPASTApplication' => 'PhabricatorApplication',
     'PhabricatorPHPConfigSetupCheck' => 'PhabricatorSetupCheck',
-    'PhabricatorPHPMailerConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorPHPPreflightSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorPackagesApplication' => 'PhabricatorApplication',
     'PhabricatorPackagesController' => 'PhabricatorController',
@@ -10331,7 +10324,6 @@ phutil_register_library_map(array(
     'PhabricatorSecuritySetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorSelectEditField' => 'PhabricatorEditField',
     'PhabricatorSelectSetting' => 'PhabricatorSetting',
-    'PhabricatorSendGridConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorSessionsSettingsPanel' => 'PhabricatorSettingsPanel',
     'PhabricatorSetConfigType' => 'PhabricatorTextConfigType',
     'PhabricatorSetting' => 'Phobject',

src/applications/config/check/PhabricatorExtraConfigSetupCheck.php

@@ -200,6 +200,9 @@ final class PhabricatorExtraConfigSetupCheck extends PhabricatorSetupCheck {
       'Elasticsearch is now configured with "%s".',
       'cluster.search');
 
+    $mailers_reason = pht(
+      'Inbound and outbound mail is now configured with "cluster.mailers".');
+
     $ancient_config += array(
       'phid.external-loaders' =>
         pht(
@@ -354,6 +357,21 @@ final class PhabricatorExtraConfigSetupCheck extends PhabricatorSetupCheck {
       'search.elastic.host' => $elastic_reason,
       'search.elastic.namespace' => $elastic_reason,
 
+      'metamta.mail-adapter' => $mailers_reason,
+      'amazon-ses.access-key' => $mailers_reason,
+      'amazon-ses.secret-key' => $mailers_reason,
+      'amazon-ses.endpoint' => $mailers_reason,
+      'mailgun.domain' => $mailers_reason,
+      'mailgun.api-key' => $mailers_reason,
+      'phpmailer.mailer' => $mailers_reason,
+      'phpmailer.smtp-host' => $mailers_reason,
+      'phpmailer.smtp-port' => $mailers_reason,
+      'phpmailer.smtp-protocol' => $mailers_reason,
+      'phpmailer.smtp-user' => $mailers_reason,
+      'phpmailer.smtp-password' => $mailers_reason,
+      'phpmailer.smtp-encoding' => $mailers_reason,
+      'sendgrid.api-user' => $mailers_reason,
+      'sendgrid.api-key' => $mailers_reason,
     );
 
     return $ancient_config;

src/applications/config/check/PhabricatorMailSetupCheck.php

@@ -1,104 +0,0 @@
-<?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;
-    }
-
-  }
-}

src/applications/config/option/PhabricatorAWSConfigOptions.php

@@ -21,24 +21,6 @@ final class PhabricatorAWSConfigOptions
 
   public function getOptions() {
     return array(
-      $this->newOption('amazon-ses.access-key', 'string', null)
-        ->setLocked(true)
-        ->setDescription(pht('Access key for Amazon SES.')),
-      $this->newOption('amazon-ses.secret-key', 'string', null)
-        ->setHidden(true)
-        ->setDescription(pht('Secret key for Amazon SES.')),
-      $this->newOption('amazon-ses.endpoint', 'string', null)
-        ->setLocked(true)
-        ->setDescription(
-          pht(
-            'SES endpoint domain name. You can find a list of available '.
-            'regions and endpoints in the AWS documentation.'))
-        ->addExample(
-          'email.us-east-1.amazonaws.com',
-          pht('US East (N. Virginia, Older default endpoint)'))
-        ->addExample(
-          'email.us-west-2.amazonaws.com',
-          pht('US West (Oregon)')),
       $this->newOption('amazon-s3.access-key', 'string', null)
         ->setLocked(true)
         ->setDescription(pht('Access key for Amazon S3.')),

src/applications/config/option/PhabricatorMailgunConfigOptions.php

@@ -1,38 +0,0 @@
-<?php
-
-final class PhabricatorMailgunConfigOptions
-  extends PhabricatorApplicationConfigOptions {
-
-  public function getName() {
-    return pht('Integration with Mailgun');
-  }
-
-  public function getDescription() {
-    return pht('Configure Mailgun integration.');
-  }
-
-  public function getIcon() {
-    return 'fa-send-o';
-  }
-
-  public function getGroup() {
-    return 'core';
-  }
-
-  public function getOptions() {
-    return array(
-      $this->newOption('mailgun.domain', 'string', null)
-        ->setLocked(true)
-        ->setDescription(
-          pht(
-            'Mailgun domain name. See %s.',
-            'https://mailgun.com/cp/domains'))
-        ->addExample('mycompany.com', pht('Use specific domain')),
-      $this->newOption('mailgun.api-key', 'string', null)
-        ->setHidden(true)
-        ->setDescription(pht('Mailgun API key.')),
-    );
-
-  }
-
-}

src/applications/config/option/PhabricatorMetaMTAConfigOptions.php

@@ -208,13 +208,6 @@ EODOC
         'string',
         'phabricator.example.com')
         ->setDescription(pht('Domain used to generate Message-IDs.')),
-      $this->newOption(
-        'metamta.mail-adapter',
-        'class',
-        'PhabricatorMailImplementationPHPMailerLiteAdapter')
-        ->setBaseClass('PhabricatorMailImplementationAdapter')
-        ->setSummary(pht('Control how mail is sent.'))
-        ->setDescription($adapter_description),
       $this->newOption(
         'metamta.one-mail-per-recipient',
         'bool',

src/applications/config/option/PhabricatorPHPMailerConfigOptions.php

@@ -1,72 +0,0 @@
-<?php
-
-final class PhabricatorPHPMailerConfigOptions
-  extends PhabricatorApplicationConfigOptions {
-
-  public function getName() {
-    return pht('PHPMailer');
-  }
-
-  public function getDescription() {
-    return pht('Configure PHPMailer.');
-  }
-
-  public function getIcon() {
-    return 'fa-send-o';
-  }
-
-  public function getGroup() {
-    return 'core';
-  }
-
-  public function getOptions() {
-    return array(
-      $this->newOption('phpmailer.mailer', 'string', 'smtp')
-        ->setLocked(true)
-        ->setSummary(pht('Configure mailer used by PHPMailer.'))
-        ->setDescription(
-          pht(
-            "If you're using PHPMailer to send email, provide the mailer and ".
-            "options here. PHPMailer is much more enormous than ".
-            "PHPMailerLite, and provides more mailers and greater enormity. ".
-            "You need it when you want to use SMTP instead of sendmail as the ".
-            "mailer.")),
-      $this->newOption('phpmailer.smtp-host', 'string', null)
-        ->setLocked(true)
-        ->setDescription(pht('Host for SMTP.')),
-      $this->newOption('phpmailer.smtp-port', 'int', 25)
-        ->setLocked(true)
-        ->setDescription(pht('Port for SMTP.')),
-      // TODO: Implement "enum"? Valid values are empty, 'tls', or 'ssl'.
-      $this->newOption('phpmailer.smtp-protocol', 'string', null)
-        ->setLocked(true)
-        ->setSummary(pht('Configure TLS or SSL for SMTP.'))
-        ->setDescription(
-          pht(
-            "Using PHPMailer with SMTP, you can set this to one of '%s' or ".
-            "'%s' to use TLS or SSL, respectively. Leave it blank for ".
-            "vanilla SMTP. If you're sending via Gmail, set it to '%s'.",
-            'tls',
-            'ssl',
-            'ssl')),
-      $this->newOption('phpmailer.smtp-user', 'string', null)
-        ->setLocked(true)
-        ->setDescription(pht('Username for SMTP.')),
-      $this->newOption('phpmailer.smtp-password', 'string', null)
-        ->setHidden(true)
-        ->setDescription(pht('Password for SMTP.')),
-      $this->newOption('phpmailer.smtp-encoding', 'string', 'base64')
-        ->setSummary(pht('Configure how mail is encoded.'))
-        ->setDescription(
-          pht(
-            "Mail is normally encoded in `8bit`, which works correctly with ".
-            "most MTAs. However, some MTAs do not work well with this ".
-            "encoding. If you're having trouble with mail being mangled or ".
-            "arriving with too many or too few newlines, you may try ".
-            "adjusting this setting.\n\n".
-            "Supported values are `8bit`, `quoted-printable`, ".
-            "`7bit`, `binary` and `base64`.")),
-    );
-  }
-
-}

src/applications/config/option/PhabricatorSendGridConfigOptions.php

@@ -1,33 +0,0 @@
-<?php
-
-final class PhabricatorSendGridConfigOptions
-  extends PhabricatorApplicationConfigOptions {
-
-  public function getName() {
-    return pht('Integration with SendGrid');
-  }
-
-  public function getDescription() {
-    return pht('Configure SendGrid integration.');
-  }
-
-  public function getIcon() {
-    return 'fa-send-o';
-  }
-
-  public function getGroup() {
-    return 'core';
-  }
-
-  public function getOptions() {
-    return array(
-      $this->newOption('sendgrid.api-user', 'string', null)
-        ->setLocked(true)
-        ->setDescription(pht('SendGrid API username.')),
-      $this->newOption('sendgrid.api-key', 'string', null)
-        ->setHidden(true)
-        ->setDescription(pht('SendGrid API key.')),
-    );
-  }
-
-}

src/applications/metamta/adapter/PhabricatorMailImplementationAdapter.php

@@ -109,7 +109,6 @@ abstract class PhabricatorMailImplementationAdapter extends Phobject {
   abstract protected function validateOptions(array $options);
 
   abstract public function newDefaultOptions();
-  abstract public function newLegacyOptions();
 
   public function prepareForSend() {
     return;

src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php

@@ -39,15 +39,6 @@ final class PhabricatorMailImplementationAmazonSESAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array(
-      'access-key' => PhabricatorEnv::getEnvConfig('amazon-ses.access-key'),
-      'secret-key' => PhabricatorEnv::getEnvConfig('amazon-ses.secret-key'),
-      'endpoint' => PhabricatorEnv::getEnvConfig('amazon-ses.endpoint'),
-      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
-    );
-  }
-
   /**
    * @phutil-external-symbol class SimpleEmailService
    */

src/applications/metamta/adapter/PhabricatorMailImplementationMailgunAdapter.php

@@ -89,13 +89,6 @@ final class PhabricatorMailImplementationMailgunAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array(
-      'api-key' => PhabricatorEnv::getEnvConfig('mailgun.api-key'),
-      'domain' => PhabricatorEnv::getEnvConfig('mailgun.domain'),
-    );
-  }
-
   public function send() {
     $key = $this->getOption('api-key');
     $domain = $this->getOption('domain');

src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerAdapter.php

@@ -33,18 +33,6 @@ final class PhabricatorMailImplementationPHPMailerAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array(
-      'host' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-host'),
-      'port' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-port'),
-      'user' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-user'),
-      'password' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-password'),
-      'protocol' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-protocol'),
-      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
-      'mailer' => PhabricatorEnv::getEnvConfig('phpmailer.mailer'),
-    );
-  }
-
   /**
    * @phutil-external-symbol class PHPMailer
    */

src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php

@@ -24,12 +24,6 @@ class PhabricatorMailImplementationPHPMailerLiteAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array(
-      'encoding' => PhabricatorEnv::getEnvConfig('phpmailer.smtp-encoding'),
-    );
-  }
-
   /**
    * @phutil-external-symbol class PHPMailerLite
    */

src/applications/metamta/adapter/PhabricatorMailImplementationPostmarkAdapter.php

@@ -94,10 +94,6 @@ final class PhabricatorMailImplementationPostmarkAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array();
-  }
-
   public function send() {
     $access_token = $this->getOption('access-token');
 

src/applications/metamta/adapter/PhabricatorMailImplementationSendGridAdapter.php

@@ -26,13 +26,6 @@ final class PhabricatorMailImplementationSendGridAdapter
     );
   }
 
-  public function newLegacyOptions() {
-    return array(
-      'api-user' => PhabricatorEnv::getEnvConfig('sendgrid.api-user'),
-      'api-key' => PhabricatorEnv::getEnvConfig('sendgrid.api-key'),
-    );
-  }
-
   public function setFrom($email, $name = '') {
     $this->params['from'] = $email;
     $this->params['from-name'] = $name;
@@ -97,18 +90,9 @@ final class PhabricatorMailImplementationSendGridAdapter
   }
 
   public function send() {
-
     $user = $this->getOption('api-user');
     $key = $this->getOption('api-key');
 
-    if (!$user || !$key) {
-      throw new Exception(
-        pht(
-          "Configure '%s' and '%s' to use SendGrid for mail delivery.",
-          'sendgrid.api-user',
-          'sendgrid.api-key'));
-    }
-
     $params = array();
 
     $ii = 0;

src/applications/metamta/adapter/PhabricatorMailImplementationTestAdapter.php

@@ -22,10 +22,6 @@ final class PhabricatorMailImplementationTestAdapter
     return array();
   }
 
-  public function newLegacyOptions() {
-    return array();
-  }
-
   public function prepareForSend(array $config = array()) {
     $this->config = $config;
   }

src/applications/metamta/storage/PhabricatorMetaMTAMail.php

@@ -520,21 +520,7 @@ final class PhabricatorMetaMTAMail
     $mailers = array();
 
     $config = PhabricatorEnv::getEnvConfig('cluster.mailers');
-    if ($config === null) {
-      $mailer = PhabricatorEnv::newObjectFromConfig('metamta.mail-adapter');
 
-      $defaults = $mailer->newDefaultOptions();
-      $options = $mailer->newLegacyOptions();
-
-      $options = $options + $defaults;
-
-      $mailer
-        ->setKey('default')
-        ->setPriority(-1)
-        ->setOptions($options);
-
-      $mailers[] = $mailer;
-    } else {
     $adapters = PhabricatorMailImplementationAdapter::getAllAdapters();
     $next_priority = -1;
 
@@ -567,7 +553,6 @@ final class PhabricatorMetaMTAMail
 
       $mailers[] = $mailer;
     }
-    }
 
     // Remove mailers with the wrong types.
     if (isset($constraints['types'])) {

src/docs/user/configuration/configuration_locked.diviner

@@ -82,7 +82,7 @@ access to fix any mistakes.
 attacker who has gained access to an administrator account in order to gain
 greater access.
 
-For example, an attacker who could modify `metamta.mail-adapter` (and other
+For example, an attacker who could modify `cluster.mailers` (and other
 similar options), could potentially reconfigure Phabricator to send mail
 through an evil server they controlled, then trigger password resets on other
 user accounts to compromise them.

src/docs/user/configuration/configuring_inbound_email.diviner

@@ -129,7 +129,7 @@ like this:
   - Add a Mailgun route with a `catch_all()` rule which takes the action
     `forward("https://phabricator.example.com/mail/mailgun/")`. Replace the
     example domain with your actual domain.
-  - Set the `mailgun.api-key` config key to your Mailgun API key.
+  - Configure a mailer in `cluster.mailers` with your Mailgun API key.
 
 Postmark Setup
 ==============