diff --git a/inmail.install b/inmail.install
index cbf3aab..fd62246 100644
--- a/inmail.install
+++ b/inmail.install
@@ -35,14 +35,12 @@ function inmail_get_plugin_requirements() {
     foreach ($enabled_instances as $enabled_instance) {
       $key = $plugin_type . '_' . $enabled_instance->id();
       $plugins[$key] = $enabled_instance->checkRequirements();
-      // Remove plugins that have no requirements.
-      // @todo: Think about improving it.
-      if ($plugins[$key] === TRUE) {
-        unset($plugins[$key]);
-      }
     }
   }
 
+  // Filter plugins with no requirements.
+  $plugins = array_filter($plugins);
+
   return $plugins;
 }
 
diff --git a/src/Entity/PluginConfigEntity.php b/src/Entity/PluginConfigEntity.php
index 0c6b26c..4f4ba18 100644
--- a/src/Entity/PluginConfigEntity.php
+++ b/src/Entity/PluginConfigEntity.php
@@ -77,6 +77,7 @@ abstract class PluginConfigEntity extends ConfigEntityBase implements PluginRequ
    * {@inheritdoc}
    */
   public function checkRequirements() {
+    $requirements = [];
     // @todo: Move to the entity level.
     $entity_type_parameters = explode('_', $this->getEntityTypeId());
     $plugin_type = end($entity_type_parameters);
@@ -89,7 +90,7 @@ abstract class PluginConfigEntity extends ConfigEntityBase implements PluginRequ
       return $plugin->checkRequirements();
     }
 
-    return TRUE;
+    return $requirements;
   }
 
 }
diff --git a/src/MessageProcessor.php b/src/MessageProcessor.php
index 4c1d209..2333b94 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() && $analyzer_config->checkRequirements() === TRUE) {
+      if ($analyzer_config->status() && empty($analyzer_config->checkRequirements())) {
         /** @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() && $handler_config->checkRequirements() === TRUE) {
+      if ($handler_config->status() && empty($handler_config->checkRequirements())) {
         /** @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 5e779a6..d18a68d 100644
--- a/src/Plugin/inmail/Analyzer/AnalyzerBase.php
+++ b/src/Plugin/inmail/Analyzer/AnalyzerBase.php
@@ -74,7 +74,7 @@ abstract class AnalyzerBase extends PluginBase implements AnalyzerInterface {
    */
   public function checkRequirements() {
     // By default, plugins have no requirements.
-    return TRUE;
+    return [];
   }
 
 }
diff --git a/src/Plugin/inmail/Deliverer/DelivererBase.php b/src/Plugin/inmail/Deliverer/DelivererBase.php
index 504444c..8c9adea 100644
--- a/src/Plugin/inmail/Deliverer/DelivererBase.php
+++ b/src/Plugin/inmail/Deliverer/DelivererBase.php
@@ -27,7 +27,7 @@ abstract class DelivererBase extends PluginBase implements DelivererInterface {
    */
   public function checkRequirements() {
     // By default, plugins have no requirements.
-    return TRUE;
+    return [];
   }
 
 }
diff --git a/src/Plugin/inmail/Handler/HandlerBase.php b/src/Plugin/inmail/Handler/HandlerBase.php
index d8683c3..e85ecc1 100644
--- a/src/Plugin/inmail/Handler/HandlerBase.php
+++ b/src/Plugin/inmail/Handler/HandlerBase.php
@@ -77,7 +77,7 @@ abstract class HandlerBase extends PluginBase implements HandlerInterface {
    */
   public function checkRequirements() {
     // By default, plugins have no requirements.
-    return TRUE;
+    return [];
   }
 
 }
diff --git a/src/PluginRequirementsInterface.php b/src/PluginRequirementsInterface.php
index 71ec7a7..a4b36d6 100644
--- a/src/PluginRequirementsInterface.php
+++ b/src/PluginRequirementsInterface.php
@@ -10,8 +10,8 @@ interface PluginRequirementsInterface {
   /**
    * Checks requirements of the current plugin.
    *
-   * @return bool|string
-   *   Returns the verbose output if requirements are not met. Otherwise, TRUE.
+   * @return array
+   *   Returns the structured verbose output if requirements are not met.
    */
   public function checkRequirements();
 
diff --git a/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php
new file mode 100644
index 0000000..d9e02e7
--- /dev/null
+++ b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/MissingRequirementAnalyzer.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\inmail_test\Plugin\inmail\Analyzer;
+
+use Drupal\inmail\DefaultAnalyzerResult;
+use Drupal\inmail\MIME\MessageInterface;
+use Drupal\inmail\Plugin\inmail\Analyzer\AnalyzerBase;
+use Drupal\inmail\ProcessorResultInterface;
+
+/**
+ * Provides an analyzer with missing requirements.
+ *
+ * @Analyzer(
+ *   id = "missing_requirement_analyzer",
+ *   label = @Translation("Missing Requirement Analyzer")
+ * )
+ */
+class MissingRequirementAnalyzer extends AnalyzerBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function analyze(MessageInterface $message, ProcessorResultInterface $processor_result) {
+    /** @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.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function checkRequirements() {
+    return [
+      'title' => $this->t('Missing test extension'),
+      'description' => $this->t('Missing Requirement Analyzer cannot be used because of missing test extension'),
+      'severity' => REQUIREMENT_ERROR,
+    ];
+  }
+
+}
diff --git a/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/TestAnalyzer.php b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/TestAnalyzer.php
index 08a0c2e..aeb12f3 100644
--- a/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/TestAnalyzer.php
+++ b/tests/modules/inmail_test/src/Plugin/inmail/Analyzer/TestAnalyzer.php
@@ -40,6 +40,9 @@ class TestAnalyzer extends AnalyzerBase {
       $demo_user->save();
     }
     $default_result->setAccount($demo_user);
+
+    // Update the body of the default result.
+    $default_result->setBody($message->getBody());
   }
 
   /**
diff --git a/tests/src/Kernel/ProcessorTest.php b/tests/src/Kernel/ProcessorTest.php
index e203425..d6a56e2 100644
--- a/tests/src/Kernel/ProcessorTest.php
+++ b/tests/src/Kernel/ProcessorTest.php
@@ -47,9 +47,9 @@ class ProcessorTest extends KernelTestBase {
   }
 
   /**
-   * Tests account switching mechanism.
+   * Tests the sample message processing.
    */
-  public function testAccountSwitching() {
+  public function testMessageProcessing() {
     $raw = <<<EOF
 Subject: Hello!
 From: Demo User <demo@example.com>
@@ -62,6 +62,10 @@ 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();
+
     HandlerConfig::create(['id' => 'result_keeper', 'plugin' => 'result_keeper'])->save();
     $processor->process($raw, DelivererConfig::create(['id' => 'test']));
 
@@ -73,6 +77,16 @@ EOF;
     $this->assertEquals('Demo User', $default_result->getAccount()->getDisplayName());
     // Assert the account was switched on handler's level.
     $this->assertEquals('Demo User', ResultKeeperHandler::getAccountName());
+
+    // Assert the requirements message.
+    $this->assertEquals([
+      'title' => t('Missing test extension'),
+      'description' => t('Missing Requirement Analyzer cannot be used because of missing test extension'),
+      'severity' => REQUIREMENT_ERROR,
+    ], $missing_requirement_analyzer->checkRequirements());
+    // The body message has not changed. It implies MissingRequirementAnalyzer
+    // did not run.
+    $this->assertEquals('Hello world!', $default_result->getBody());
   }
 
 }