diff --git a/src/Service/VersionService.php b/src/Service/VersionService.php
index c6b36f5..b696709 100644
--- a/src/Service/VersionService.php
+++ b/src/Service/VersionService.php
@@ -15,6 +15,7 @@
 use TYPO3\Tailor\Environment\Variables;
 use TYPO3\Tailor\Exception\FormDataProcessingException;
 use TYPO3\Tailor\Exception\RequiredConfigurationMissing;
+use TYPO3\Tailor\Validation\EmConfValidationError;
 use TYPO3\Tailor\Validation\EmConfVersionValidator;
 use ZipArchive;
 
@@ -63,7 +64,7 @@ public function createZipArchiveFromPath(string $path): string
         $zipArchive = new \ZipArchive();
         $zipArchive->open($this->getVersionFilename(), \ZipArchive::CREATE | \ZipArchive::OVERWRITE);
 
-        $emConfValid = false;
+        $emConfValidationErrors = [EmConfValidationError::NOT_FOUND];
 
         $iterator = new \RecursiveDirectoryIterator($fullPath, \FilesystemIterator::SKIP_DOTS);
         $files = new \RecursiveIteratorIterator(
@@ -110,15 +111,15 @@ public function createZipArchiveFromPath(string $path): string
             }
 
             if ($filename === 'ext_emconf.php') {
-                $emConfValid = (new EmConfVersionValidator($fileRealPath))->isValid($this->version);
+                $emConfValidationErrors = (new EmConfVersionValidator($fileRealPath))->collectErrors($this->version);
             }
 
             // Add the files including their directories
             $zipArchive->addFile($fileRealPath, substr($fileRealPath, strlen($fullPath) + 1));
         }
 
-        if (!$emConfValid) {
-            throw new FormDataProcessingException('No or invalid ext_emconf.php found in the folder.', 1605563410);
+        if ($emConfValidationErrors !== []) {
+            throw new FormDataProcessingException($this->formatEmConfValidationErrors($emConfValidationErrors), 1605563410);
         }
 
         $zipArchive->close();
@@ -233,4 +234,18 @@ protected function getExcludeConfiguration(): array
 
         return $configuration;
     }
+
+    /**
+     * @param list<EmConfValidationError::*> $errors
+     */
+    private function formatEmConfValidationErrors(array $errors): string
+    {
+        $messageParts = ['Validation of `ext_emconf.php` file failed due to the following errors:'];
+
+        foreach ($errors as $error) {
+            $messageParts[] = '  * ' . EmConfValidationError::getErrorMessage($error);
+        }
+
+        return implode(PHP_EOL, $messageParts);
+    }
 }
diff --git a/src/Validation/EmConfValidationError.php b/src/Validation/EmConfValidationError.php
new file mode 100644
index 0000000..3edab7b
--- /dev/null
+++ b/src/Validation/EmConfValidationError.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the TYPO3 project  - inspiring people to share!
+ * (c) 2020 Oliver Bartsch & Benni Mack
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace TYPO3\Tailor\Validation;
+
+/**
+ * Enum with validation errors of ext_emconf.php files.
+ *
+ * @todo Convert to native enum once support for PHP < 8.1 is dropped.
+ */
+abstract class EmConfValidationError
+{
+    public const EXTENSION_VERSION_MISMATCH = 'extension-version-mismatch';
+    public const MISSING_CONFIGURATION = 'missing-configuration';
+    public const MISSING_EXTENSION_VERSION = 'missing-version';
+    public const MISSING_TYPO3_VERSION_CONSTRAINT = 'missing-typo3-version-constraint';
+    public const NOT_FOUND = 'not-found';
+    public const UNSUPPORTED_TYPE = 'unsupported-type';
+
+    public static function getErrorMessage(string $error): string
+    {
+        switch ($error) {
+            case self::EXTENSION_VERSION_MISMATCH:
+                return 'The configured version in `ext_emconf.php` file does not match the given version for release.';
+            case self::MISSING_CONFIGURATION:
+                return 'The `ext_emconf.php` file is missing an $EM_CONF configuration array.';
+            case self::MISSING_EXTENSION_VERSION:
+                return 'No version configured in `ext_emconf.php` file.';
+            case self::MISSING_TYPO3_VERSION_CONSTRAINT:
+                return 'No TYPO3 version constraint configured in `ext_emconf.php` file.';
+            case self::NOT_FOUND:
+                return 'No `ext_emconf.php` file found in the folder.';
+            case self::UNSUPPORTED_TYPE:
+                return 'The $EM_CONF variable in `ext_emconf.php` file contains an unsupported type (should be an array).';
+            default:
+                // @todo Can be removed once this class is converted to a native enum.
+                return 'An unexpected error occurred while reading the `ext_emconf.php` file.';
+        }
+    }
+}
diff --git a/src/Validation/EmConfVersionValidator.php b/src/Validation/EmConfVersionValidator.php
index cee82ea..bc0c53a 100644
--- a/src/Validation/EmConfVersionValidator.php
+++ b/src/Validation/EmConfVersionValidator.php
@@ -32,26 +32,47 @@ public function __construct(string $filePath)
     }
 
     /**
-     * @param string $givenVersion
-     * @return bool TRUE if the ext_emconf is valid, FALSE otherwise
+     * @return list<EmConfValidationError::*> List of validation errors. If list is empty, ext_emconf.php file is valid.
      */
-    public function isValid(string $givenVersion): bool
+    public function collectErrors(string $givenVersion): array
     {
+        if (!file_exists($this->emConfFilePath)) {
+            return [EmConfValidationError::NOT_FOUND];
+        }
+
         $_EXTKEY = 'dummy';
         @include $this->emConfFilePath;
+
         if (!isset($EM_CONF)) {
-            return false;
+            return [EmConfValidationError::MISSING_CONFIGURATION];
         }
+
         $emConfDetails = reset($EM_CONF);
+
         if (!is_array($emConfDetails)) {
-            return false;
+            return [EmConfValidationError::UNSUPPORTED_TYPE];
         }
-        if (!isset($emConfDetails['version'], $emConfDetails['constraints']['depends']['typo3'])) {
-            return false;
+
+        $errors = [];
+
+        if (!isset($emConfDetails['version'])) {
+            $errors[] = EmConfValidationError::MISSING_EXTENSION_VERSION;
+        } elseif ((string)$emConfDetails['version'] !== $givenVersion) {
+            $errors[] = EmConfValidationError::EXTENSION_VERSION_MISMATCH;
         }
-        if ((string)$emConfDetails['version'] !== $givenVersion) {
-            return false;
+        if (!isset($emConfDetails['constraints']['depends']['typo3'])) {
+            $errors[] = EmConfValidationError::MISSING_TYPO3_VERSION_CONSTRAINT;
         }
-        return true;
+
+        return $errors;
+    }
+
+    /**
+     * @param string $givenVersion
+     * @return bool TRUE if the ext_emconf is valid, FALSE otherwise
+     */
+    public function isValid(string $givenVersion): bool
+    {
+        return $this->collectErrors($givenVersion) === [];
     }
 }
diff --git a/tests/Unit/Fixtures/EmConf/emconf_no_version.php b/tests/Unit/Fixtures/EmConf/emconf_no_version.php
index ddd457c..6d551c8 100644
--- a/tests/Unit/Fixtures/EmConf/emconf_no_version.php
+++ b/tests/Unit/Fixtures/EmConf/emconf_no_version.php
@@ -1,5 +1,5 @@
 <?php
 
-$EM_CONF = [
+$EM_CONF[$_EXTKEY] = [
     'nothing' => 'YES',
 ];
diff --git a/tests/Unit/Validation/EmConfVersionValidatorTest.php b/tests/Unit/Validation/EmConfVersionValidatorTest.php
index f8c7212..a5559b2 100644
--- a/tests/Unit/Validation/EmConfVersionValidatorTest.php
+++ b/tests/Unit/Validation/EmConfVersionValidatorTest.php
@@ -13,10 +13,73 @@
 namespace TYPO3\Tailor\Tests\Unit\Validation;
 
 use PHPUnit\Framework\TestCase;
+use TYPO3\Tailor\Validation\EmConfValidationError;
 use TYPO3\Tailor\Validation\EmConfVersionValidator;
 
 class EmConfVersionValidatorTest extends TestCase
 {
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsErrorIfFileDoesNotExist(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/no-file');
+        $expected = [EmConfValidationError::NOT_FOUND];
+        self::assertSame($expected, $subject->collectErrors('1.2.0'));
+    }
+
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsErrorIfConfigurationIsMissing(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/../Fixtures/EmConf/emconf_invalid.php');
+        $expected = [EmConfValidationError::MISSING_CONFIGURATION];
+        self::assertSame($expected, $subject->collectErrors('1.0.0'));
+    }
+
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsErrorIfFileDoesNotMatchEmConfStructure(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/../Fixtures/EmConf/emconf_no_structure.php');
+        $expected = [EmConfValidationError::UNSUPPORTED_TYPE];
+        self::assertSame($expected, $subject->collectErrors('1.0.0'));
+    }
+
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsErrorsIfNoVersionGiven(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/../Fixtures/EmConf/emconf_no_version.php');
+        $expected = [
+            EmConfValidationError::MISSING_EXTENSION_VERSION,
+            EmConfValidationError::MISSING_TYPO3_VERSION_CONSTRAINT,
+        ];
+        self::assertSame($expected, $subject->collectErrors('1.0.0'));
+    }
+
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsErrorIfVersionsDoNotMatch(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/../Fixtures/EmConf/emconf_valid.php');
+        $expected = [EmConfValidationError::EXTENSION_VERSION_MISMATCH];
+        self::assertSame($expected, $subject->collectErrors('2.0.0'));
+    }
+
+    /**
+     * @test
+     */
+    public function collectErrorsReturnsEmptyArrayIfFileIsValid(): void
+    {
+        $subject = new EmConfVersionValidator(__DIR__ . '/../Fixtures/EmConf/emconf_valid.php');
+        self::assertSame([], $subject->collectErrors('1.0.0'));
+    }
+
     /**
      * @test
      */