diff --git a/inmail.install b/inmail.install
index fd62246..61a4396 100644
--- a/inmail.install
+++ b/inmail.install
@@ -3,7 +3,6 @@
  * @file
  * Implementations of install hooks for the Inmail module.
  */
-use Drupal\inmail\PluginRequirementsInterface;
 
 /**
  * Implements hook_requirements().
@@ -27,21 +26,22 @@ function inmail_get_plugin_requirements() {
   /** @var \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager */
   $entity_type_manager = \Drupal::entityTypeManager();
   $plugin_types = ['analyzer', 'deliverer', 'handler'];
-  $plugins = [];
+  $plugin_requirements = [];
 
   foreach ($plugin_types as $plugin_type) {
     $enabled_instances = $entity_type_manager->getStorage("inmail_$plugin_type")->loadByProperties(['status' => TRUE]);
     /** @var \Drupal\inmail\Entity\PluginConfigEntity $enabled_instance */
     foreach ($enabled_instances as $enabled_instance) {
-      $key = $plugin_type . '_' . $enabled_instance->id();
-      $plugins[$key] = $enabled_instance->checkRequirements();
+      if (!$enabled_instance->isAvailable()) {
+        $key = $plugin_type . '_' . $enabled_instance->getPluginId();
+        if (!isset($plugin_requirements[$key])) {
+          $plugin_requirements[$key] = $enabled_instance->checkRequirements();
+        }
+      }
     }
   }
 
-  // Filter plugins with no requirements.
-  $plugins = array_filter($plugins);
-
-  return $plugins;
+  return $plugin_requirements;
 }
 
 /**
diff --git a/src/Entity/AnalyzerConfig.php b/src/Entity/AnalyzerConfig.php
index b415afb..90e4873 100644
--- a/src/Entity/AnalyzerConfig.php
+++ b/src/Entity/AnalyzerConfig.php
@@ -43,6 +43,20 @@ namespace Drupal\inmail\Entity;
 class AnalyzerConfig extends PluginConfigEntity {
 
   /**
+   * Constructs a new AnalyzerConfig.
+   *
+   * @param array $values
+   *   An array of values to set, keyed by property name. If the entity type
+   *   has bundles, the bundle key has to be specified.
+   * @param string $entity_type
+   *   The type of the entity to create.
+   */
+  public function __construct(array $values, $entity_type) {
+    parent::__construct($values, $entity_type);
+    $this->pluginType = 'analyzer';
+  }
+
+  /**
    * The weight of the analyzer configuration.
    *
    * Analyzers with lower weights are invoked before those with higher weights.
diff --git a/src/Entity/DelivererConfig.php b/src/Entity/DelivererConfig.php
index 39893d0..0cbed0a 100644
--- a/src/Entity/DelivererConfig.php
+++ b/src/Entity/DelivererConfig.php
@@ -40,4 +40,18 @@ namespace Drupal\inmail\Entity;
  * )
  */
 class DelivererConfig extends PluginConfigEntity {
+
+  /**
+   * Constructs a new DelivererConfig.
+   *
+   * @param array $values
+   *   An array of values to set, keyed by property name. If the entity type
+   *   has bundles, the bundle key has to be specified.
+   * @param string $entity_type
+   *   The type of the entity to create.
+   */
+  public function __construct(array $values, $entity_type) {
+    parent::__construct($values, $entity_type);
+    $this->pluginType = 'deliverer';
+  }
 }
diff --git a/src/Entity/HandlerConfig.php b/src/Entity/HandlerConfig.php
index 552f146..0344acb 100644
--- a/src/Entity/HandlerConfig.php
+++ b/src/Entity/HandlerConfig.php
@@ -40,4 +40,19 @@ namespace Drupal\inmail\Entity;
  */
 class HandlerConfig extends PluginConfigEntity {
   // @todo Implement HandlerConfig::calculateDependencies() https://www.drupal.org/node/2379929
+
+  /**
+   * Constructs a new HandlerConfig.
+   *
+   * @param array $values
+   *   An array of values to set, keyed by property name. If the entity type
+   *   has bundles, the bundle key has to be specified.
+   * @param string $entity_type
+   *   The type of the entity to create.
+   */
+  public function __construct(array $values, $entity_type) {
+    parent::__construct($values, $entity_type);
+    $this->pluginType = 'handler';
+  }
+
 }
diff --git a/src/Entity/PluginConfigEntity.php b/src/Entity/PluginConfigEntity.php
index 4f4ba18..f704a3d 100644
--- a/src/Entity/PluginConfigEntity.php
+++ b/src/Entity/PluginConfigEntity.php
@@ -39,6 +39,20 @@ abstract class PluginConfigEntity extends ConfigEntityBase implements PluginRequ
   protected $configuration = array();
 
   /**
+   * The plugin instance.
+   *
+   * @var \Drupal\inmail\Plugin\inmail\Analyzer\AnalyzerInterface|\Drupal\inmail\Plugin\inmail\Deliverer\DelivererInterface|\Drupal\inmail\Plugin\inmail\Handler\HandlerInterface
+   */
+  protected $pluginInstance;
+
+  /**
+   * The Inmail plugin type - deliverer, analyzer, handler.
+   *
+   * @var string
+   */
+  protected $pluginType;
+
+  /**
    * Returns the plugin ID.
    *
    * @return string
@@ -74,23 +88,52 @@ abstract class PluginConfigEntity extends ConfigEntityBase implements PluginRequ
   }
 
   /**
+   * Returns the plugin instance.
+   *
+   * @return \Drupal\inmail\Plugin\inmail\Analyzer\AnalyzerInterface|\Drupal\inmail\Plugin\inmail\Deliverer\DelivererInterface|\Drupal\inmail\Plugin\inmail\Handler\HandlerInterface
+   *   The instantiated plugin.
+   */
+  public function getPluginInstance() {
+    if (empty($this->pluginInstance)) {
+      return \Drupal::service('plugin.manager.inmail.' . $this->pluginType)->createInstance($this->plugin, $this->configuration);
+    }
+
+    return $this->pluginInstance;
+  }
+
+  /**
+   * Returns the plugin type.
+   *
+   * @return string
+   *   The plugin type.
+   */
+  public function getPluginType() {
+    return $this->pluginType;
+  }
+
+  /**
    * {@inheritdoc}
    */
   public function checkRequirements() {
     $requirements = [];
-    // @todo: Move to the entity level.
-    $entity_type_parameters = explode('_', $this->getEntityTypeId());
-    $plugin_type = end($entity_type_parameters);
-
-    /** @var \Drupal\Core\Plugin\DefaultPluginManager $plugin_manager */
-    $plugin_manager = \Drupal::service("plugin.manager.inmail.$plugin_type");
-    // Create plugin instance.
-    // @todo: Implement getPlugin() method.
-    if ($plugin = $plugin_manager->createInstance($this->getPluginId(), $this->getConfiguration())) {
+
+    if ($plugin = $this->getPluginInstance()) {
       return $plugin->checkRequirements();
     }
 
     return $requirements;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function isAvailable() {
+    $is_available = FALSE;
+    if ($plugin = $this->getPluginInstance()) {
+      $is_available = $plugin->isAvailable();
+    }
+
+    return $is_available;
+  }
+
 }
diff --git a/src/MessageProcessor.php b/src/MessageProcessor.php
index 2333b94..ef7abd3 100644
--- a/src/MessageProcessor.php
+++ b/src/MessageProcessor.php
@@ -115,7 +115,7 @@ class MessageProcessor implements MessageProcessorInterface {
     uasort($analyzer_configs, array($this->analyzerStorage->getEntityType()->getClass(), 'sort'));
     foreach ($analyzer_configs as $analyzer_config) {
       /** @var \Drupal\inmail\Entity\AnalyzerConfig $analyzer_config */
-      if ($analyzer_config->status() && empty($analyzer_config->checkRequirements())) {
+      if ($analyzer_config->status() && $analyzer_config->isAvailable()) {
         /** @var \Drupal\inmail\Plugin\inmail\Analyzer\AnalyzerInterface $analyzer */
         $analyzer = $this->analyzerManager->createInstance($analyzer_config->getPluginId(), $analyzer_config->getConfiguration());
         $analyzer->analyze($message, $result);
@@ -136,7 +136,7 @@ class MessageProcessor implements MessageProcessorInterface {
     // Handle message.
     foreach ($this->handlerStorage->loadMultiple() as $handler_config) {
       /** @var \Drupal\inmail\Entity\HandlerConfig $handler_config */
-      if ($handler_config->status() && empty($handler_config->checkRequirements())) {
+      if ($handler_config->status() && $handler_config->isAvailable()) {
         /** @var \Drupal\inmail\Plugin\inmail\handler\HandlerInterface $handler */
         $handler = $this->handlerManager->createInstance($handler_config->getPluginId(), $handler_config->getConfiguration());
         $handler->invoke($message, $result);
diff --git a/src/Plugin/inmail/Analyzer/AnalyzerBase.php b/src/Plugin/inmail/Analyzer/AnalyzerBase.php
index d18a68d..f83e830 100644
--- a/src/Plugin/inmail/Analyzer/AnalyzerBase.php
+++ b/src/Plugin/inmail/Analyzer/AnalyzerBase.php
@@ -3,7 +3,7 @@
 namespace Drupal\inmail\Plugin\inmail\Analyzer;
 
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Plugin\PluginBase;
+use Drupal\inmail\PluginBase;
 
 /**
  * Base class for message analyzer plugins.
@@ -69,12 +69,4 @@ abstract class AnalyzerBase extends PluginBase implements AnalyzerInterface {
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function checkRequirements() {
-    // By default, plugins have no requirements.
-    return [];
-  }
-
 }
diff --git a/src/Plugin/inmail/Analyzer/AnalyzerInterface.php b/src/Plugin/inmail/Analyzer/AnalyzerInterface.php
index 7891bd8..2d2af2f 100644
--- a/src/Plugin/inmail/Analyzer/AnalyzerInterface.php
+++ b/src/Plugin/inmail/Analyzer/AnalyzerInterface.php
@@ -6,7 +6,6 @@ use Drupal\Component\Plugin\ConfigurablePluginInterface;
 use Drupal\Component\Plugin\PluginInspectionInterface;
 use Drupal\Core\Plugin\PluginFormInterface;
 use Drupal\inmail\MIME\MessageInterface;
-use Drupal\inmail\PluginRequirementsInterface;
 use Drupal\inmail\ProcessorResultInterface;
 
 /**
@@ -14,7 +13,7 @@ use Drupal\inmail\ProcessorResultInterface;
  *
  * @ingroup analyzer
  */
-interface AnalyzerInterface extends ConfigurablePluginInterface, PluginFormInterface, PluginInspectionInterface, PluginRequirementsInterface {
+interface AnalyzerInterface extends ConfigurablePluginInterface, PluginFormInterface, PluginInspectionInterface {
 
   /**
    * Analyze the given message.
diff --git a/src/Plugin/inmail/Deliverer/DelivererBase.php b/src/Plugin/inmail/Deliverer/DelivererBase.php
index 8c9adea..412dce4 100644
--- a/src/Plugin/inmail/Deliverer/DelivererBase.php
+++ b/src/Plugin/inmail/Deliverer/DelivererBase.php
@@ -1,8 +1,7 @@
 <?php
 
 namespace Drupal\inmail\Plugin\inmail\Deliverer;
-
-use Drupal\Core\Plugin\PluginBase;
+use Drupal\inmail\PluginBase;
 
 /**
  * Base class for mail deliverers.
@@ -22,12 +21,4 @@ abstract class DelivererBase extends PluginBase implements DelivererInterface {
     return $this->pluginDefinition['label'];
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function checkRequirements() {
-    // By default, plugins have no requirements.
-    return [];
-  }
-
 }
diff --git a/src/Plugin/inmail/Deliverer/DelivererInterface.php b/src/Plugin/inmail/Deliverer/DelivererInterface.php
index 9df55d4..81a35ea 100644
--- a/src/Plugin/inmail/Deliverer/DelivererInterface.php
+++ b/src/Plugin/inmail/Deliverer/DelivererInterface.php
@@ -3,7 +3,6 @@
 namespace Drupal\inmail\Plugin\inmail\Deliverer;
 
 use Drupal\Component\Plugin\PluginInspectionInterface;
-use Drupal\inmail\PluginRequirementsInterface;
 
 /**
  * Defines methods for deliverers.
@@ -12,7 +11,7 @@ use Drupal\inmail\PluginRequirementsInterface;
  *
  * @ingroup deliverer
  */
-interface DelivererInterface extends PluginInspectionInterface, PluginRequirementsInterface {
+interface DelivererInterface extends PluginInspectionInterface {
 
   /**
    * Returns the deliverer label.
diff --git a/src/Plugin/inmail/Handler/HandlerBase.php b/src/Plugin/inmail/Handler/HandlerBase.php
index e85ecc1..5e3dce3 100644
--- a/src/Plugin/inmail/Handler/HandlerBase.php
+++ b/src/Plugin/inmail/Handler/HandlerBase.php
@@ -3,7 +3,7 @@
 namespace Drupal\inmail\Plugin\inmail\Handler;
 
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Plugin\PluginBase;
+use Drupal\inmail\PluginBase;
 
 /**
  * Base class for message handler plugins.
@@ -72,12 +72,4 @@ abstract class HandlerBase extends PluginBase implements HandlerInterface {
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function checkRequirements() {
-    // By default, plugins have no requirements.
-    return [];
-  }
-
 }
diff --git a/src/Plugin/inmail/Handler/HandlerInterface.php b/src/Plugin/inmail/Handler/HandlerInterface.php
index 240657a..b89b065 100644
--- a/src/Plugin/inmail/Handler/HandlerInterface.php
+++ b/src/Plugin/inmail/Handler/HandlerInterface.php
@@ -6,7 +6,6 @@ use Drupal\Component\Plugin\ConfigurablePluginInterface;
 use Drupal\Component\Plugin\PluginInspectionInterface;
 use Drupal\Core\Plugin\PluginFormInterface;
 use Drupal\inmail\MIME\MessageInterface;
-use Drupal\inmail\PluginRequirementsInterface;
 use Drupal\inmail\ProcessorResultInterface;
 
 /**
@@ -14,7 +13,7 @@ use Drupal\inmail\ProcessorResultInterface;
  *
  * @ingroup handler
  */
-interface HandlerInterface extends ConfigurablePluginInterface, PluginFormInterface, PluginInspectionInterface, PluginRequirementsInterface {
+interface HandlerInterface extends ConfigurablePluginInterface, PluginFormInterface, PluginInspectionInterface {
 
   /**
    * Returns helpful explanation for using and configuring the handler.
diff --git a/src/PluginBase.php b/src/PluginBase.php
new file mode 100644
index 0000000..a5914e3
--- /dev/null
+++ b/src/PluginBase.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Drupal\inmail;
+
+use Drupal\Core\Plugin\PluginBase as CorePluginBase;
+
+/**
+ * Base class for Inmail plugins - deliverers, analyzers, handlers.
+ */
+abstract class PluginBase extends CorePluginBase implements PluginRequirementsInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function checkRequirements() {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isAvailable() {
+    return TRUE;
+  }
+
+}
diff --git a/src/PluginRequirementsInterface.php b/src/PluginRequirementsInterface.php
index a4b36d6..052bcf4 100644
--- a/src/PluginRequirementsInterface.php
+++ b/src/PluginRequirementsInterface.php
@@ -12,7 +12,16 @@ interface PluginRequirementsInterface {
    *
    * @return array
    *   Returns the structured verbose output if requirements are not met.
+   *   In case of no plugin requirements, an empty array is returned.
    */
   public function checkRequirements();
 
+  /**
+   * Flag determining whether a plugin is available to be used in processing.
+   *
+   * @return bool
+   *   TRUE if the plugin is available. Otherwise, FALSE.
+   */
+  public function isAvailable();
+
 }
diff --git a/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/UnavailableAnalyzer.php
similarity index 55%
rename from tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php
rename to tests/modules/inmail_test/src/Plugin/inmail/Analyzer/UnavailableAnalyzer.php
index d9e02e7..9076853 100644
--- a/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php
+++ b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/UnavailableAnalyzer.php
@@ -8,14 +8,14 @@ use Drupal\inmail\Plugin\inmail\Analyzer\AnalyzerBase;
 use Drupal\inmail\ProcessorResultInterface;
 
 /**
- * Provides an analyzer with missing requirements.
+ * Provides an unavailable analyzer.
  *
  * @Analyzer(
- *   id = "missing_requirement_analyzer",
- *   label = @Translation("Missing Requirement Analyzer")
+ *   id = "unavailable_analyzer",
+ *   label = @Translation("Unavailable Analyzer")
  * )
  */
-class MissingRequirementAnalyzer extends AnalyzerBase {
+class UnavailableAnalyzer extends AnalyzerBase {
 
   /**
    * {@inheritdoc}
@@ -24,9 +24,9 @@ class MissingRequirementAnalyzer extends AnalyzerBase {
     /** @var \Drupal\inmail\DefaultAnalyzerResult $default_result */
     $default_result = $processor_result->getAnalyzerResult(DefaultAnalyzerResult::TOPIC);
 
-    // Do the fake body update. This should not be executed because of the
-    // plugin requirements check.
-    $default_result->setBody('The body has been updated by MissingRequirementAnalyzer.');
+    // Do the fake body update. This should not be executed as we only execute
+    // available analyzers.
+    $default_result->setBody('The body has been updated by UnavailableAnalyzer.');
   }
 
   /**
@@ -34,10 +34,17 @@ class MissingRequirementAnalyzer extends AnalyzerBase {
    */
   public function checkRequirements() {
     return [
-      'title' => $this->t('Missing test extension'),
-      'description' => $this->t('Missing Requirement Analyzer cannot be used because of missing test extension'),
+      'title' => $this->t('Unavailable Analyzer'),
+      'description' => $this->t('Unavailable Analyzer cannot be used.'),
       'severity' => REQUIREMENT_ERROR,
     ];
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function isAvailable() {
+    return FALSE;
+  }
+
 }
diff --git a/tests/src/Kernel/ProcessorTest.php b/tests/src/Kernel/ProcessorTest.php
index d6a56e2..f385fb1 100644
--- a/tests/src/Kernel/ProcessorTest.php
+++ b/tests/src/Kernel/ProcessorTest.php
@@ -62,9 +62,9 @@ EOF;
     $processor = \Drupal::service('inmail.processor');
 
     AnalyzerConfig::create(['id' => 'test_analyzer', 'plugin' => 'test_analyzer'])->save();
-    // Add an analyzer with missing requirements.
-    $missing_requirement_analyzer = AnalyzerConfig::create(['id' => 'missing_requirement_analyzer', 'plugin' => 'missing_requirement_analyzer']);
-    $missing_requirement_analyzer->save();
+    // Add an unavailable analyzer.
+    $unavailable_analyzer = AnalyzerConfig::create(['id' => 'unavailable_analyzer', 'plugin' => 'unavailable_analyzer']);
+    $unavailable_analyzer->save();
 
     HandlerConfig::create(['id' => 'result_keeper', 'plugin' => 'result_keeper'])->save();
     $processor->process($raw, DelivererConfig::create(['id' => 'test']));
@@ -80,11 +80,12 @@ EOF;
 
     // Assert the requirements message.
     $this->assertEquals([
-      'title' => t('Missing test extension'),
-      'description' => t('Missing Requirement Analyzer cannot be used because of missing test extension'),
+      'title' => t('Unavailable Analyzer'),
+      'description' => t('Unavailable Analyzer cannot be used.'),
       'severity' => REQUIREMENT_ERROR,
-    ], $missing_requirement_analyzer->checkRequirements());
-    // The body message has not changed. It implies MissingRequirementAnalyzer
+    ], $unavailable_analyzer->checkRequirements());
+    $this->assertEquals(FALSE, $unavailable_analyzer->isAvailable());
+    // The body message has not changed. It implies UnavailableAnalyzer
     // did not run.
     $this->assertEquals('Hello world!', $default_result->getBody());
   }