diff --git a/de.systopia.civiproxy/Civi/CiviProxy/CompilerPass.php b/de.systopia.civiproxy/Civi/CiviProxy/CompilerPass.php
new file mode 100644
index 0000000..1c3a3bc
--- /dev/null
+++ b/de.systopia.civiproxy/Civi/CiviProxy/CompilerPass.php
@@ -0,0 +1,26 @@
+<?php
+/**
+ * @author Jaap Jansma <jaap.jansma@civicoop.org>
+ * @license AGPL-3.0
+ */
+namespace Civi\CiviProxy;
+
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Definition;
+
+class CompilerPass implements CompilerPassInterface {
+
+  /**
+   * You can modify the container here before it is dumped to PHP code.
+   */
+  public function process(ContainerBuilder $container) {
+    if (!$container->hasDefinition('data_processor_factory')) {
+      return;
+    }
+    $factoryDefinition = $container->getDefinition('data_processor_factory');
+    $factoryDefinition->addMethodCall('addOutputHandler', array('civiproxy_file_field', 'Civi\CiviProxy\DataProcessor\FileFieldOutputHandler', ts('CiviProxy File download link')));
+  }
+
+
+}
diff --git a/de.systopia.civiproxy/Civi/CiviProxy/DataProcessor/FileFieldOutputHandler.php b/de.systopia.civiproxy/Civi/CiviProxy/DataProcessor/FileFieldOutputHandler.php
new file mode 100644
index 0000000..d4e142b
--- /dev/null
+++ b/de.systopia.civiproxy/Civi/CiviProxy/DataProcessor/FileFieldOutputHandler.php
@@ -0,0 +1,184 @@
+<?php
+/**
+ * @author Jaap Jansma <jaap.jansma@civicoop.org>
+ * @license AGPL-3.0
+ */
+
+namespace Civi\CiviProxy\DataProcessor;
+
+use Civi\DataProcessor\FieldOutputHandler\AbstractFieldOutputHandler;
+use Civi\DataProcessor\Source\SourceInterface;
+use Civi\DataProcessor\DataSpecification\FieldSpecification;
+use Civi\DataProcessor\FieldOutputHandler\FieldOutput;
+use Civi\DataProcessor\Exception\DataSourceNotFoundException;
+use Civi\DataProcessor\Exception\FieldNotFoundException;
+
+class FileFieldOutputHandler extends AbstractFieldOutputHandler {
+
+  /**
+   * Returns the data type of this field
+   *
+   * @return String
+   */
+  protected function getType() {
+    return 'String';
+  }
+
+  /**
+   * Returns the formatted value
+   *
+   * @param $rawRecord
+   * @param $formattedRecord
+   *
+   * @return \Civi\DataProcessor\FieldOutputHandler\FieldOutput
+   */
+  public function formatField($rawRecord, $formattedRecord) {
+    $rawValue = $rawRecord[$this->inputFieldSpec->alias];
+    $output = new FieldOutput($rawValue);
+    if ($rawValue) {
+      $proxy_base  = \CRM_Core_BAO_Setting::getItem('CiviProxy Settings', 'proxy_url');
+      $attachment = civicrm_api3('Attachment', 'getsingle', array('id' => $rawValue));
+      if (!isset($attachment['is_error']) || $attachment['is_error'] == '0') {
+        $fcs = \CRM_Core_BAO_File::generateFileHash($attachment['entity_id'], $attachment['id']);
+        $output->formattedValue = $proxy_base.'/file.php?id='.$attachment['id'].'&eid='.$attachment['entity_id'].'&fcs='.$fcs;
+      }
+    }
+    return $output;
+  }
+
+  /**
+   * Callback function for determining whether this field could be handled by this output handler.
+   *
+   * @param \Civi\DataProcessor\DataSpecification\FieldSpecification $field
+   * @return bool
+   */
+  public function isFieldValid(FieldSpecification $field) {
+    if ($field->type == 'File') {
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * @var \Civi\DataProcessor\DataSpecification\FieldSpecification
+   */
+  protected $inputFieldSpec;
+
+  /**
+   * @var \Civi\DataProcessor\DataSpecification\FieldSpecification
+   */
+  protected $outputFieldSpec;
+
+  /**
+   * @var SourceInterface
+   */
+  protected $dataSource;
+
+  /**
+   * @return \Civi\DataProcessor\DataSpecification\FieldSpecification
+   */
+  public function getOutputFieldSpecification() {
+    return $this->outputFieldSpec;
+  }
+
+  /**
+   * Initialize the processor
+   *
+   * @param String $alias
+   * @param String $title
+   * @param array $configuration
+   * @param \Civi\DataProcessor\ProcessorType\AbstractProcessorType $processorType
+   */
+  public function initialize($alias, $title, $configuration) {
+    $this->dataSource = $this->dataProcessor->getDataSourceByName($configuration['datasource']);
+    if (!$this->dataSource) {
+      throw new DataSourceNotFoundException(ts("Field %1 requires data source '%2' which could not be found. Did you rename or deleted the data source?", array(1=>$title, 2=>$configuration['datasource'])));
+    }
+    $this->inputFieldSpec = $this->dataSource->getAvailableFields()->getFieldSpecificationByName($configuration['field']);
+    if (!$this->inputFieldSpec) {
+      throw new FieldNotFoundException(ts("Field %1 requires a field with the name '%2' in the data source '%3'. Did you change the data source type?", array(
+        1 => $title,
+        2 => $configuration['field'],
+        3 => $configuration['datasource']
+      )));
+    }
+    $this->dataSource->ensureFieldInSource($this->inputFieldSpec);
+
+    $this->outputFieldSpec = clone $this->inputFieldSpec;
+    $this->outputFieldSpec->alias = $alias;
+    $this->outputFieldSpec->title = $title;
+  }
+
+  /**
+   * Returns true when this handler has additional configuration.
+   *
+   * @return bool
+   */
+  public function hasConfiguration() {
+    return true;
+  }
+
+  /**
+   * When this handler has additional configuration you can add
+   * the fields on the form with this function.
+   *
+   * @param \CRM_Core_Form $form
+   * @param array $field
+   */
+  public function buildConfigurationForm(\CRM_Core_Form $form, $field=array()) {
+    $fieldSelect = $this->getFieldOptions($field['data_processor_id']);
+
+    $form->add('select', 'field', ts('Field'), $fieldSelect, true, array(
+      'style' => 'min-width:250px',
+      'class' => 'crm-select2 huge data-processor-field-for-name',
+      'placeholder' => ts('- select -'),
+    ));
+    if (isset($field['configuration'])) {
+      $configuration = $field['configuration'];
+      $defaults = array();
+      if (isset($configuration['field']) && isset($configuration['datasource'])) {
+        $defaults['field'] = $configuration['datasource'] . '::' . $configuration['field'];
+      }
+      $form->setDefaults($defaults);
+    }
+  }
+
+  /**
+   * When this handler has configuration specify the template file name
+   * for the configuration form.
+   *
+   * @return false|string
+   */
+  public function getConfigurationTemplateFileName() {
+    return "CRM/Dataprocessor/Form/Field/Configuration/RawFieldOutputHandler.tpl";
+  }
+
+
+  /**
+   * Process the submitted values and create a configuration array
+   *
+   * @param $submittedValues
+   * @return array
+   */
+  public function processConfiguration($submittedValues) {
+    list($datasource, $field) = explode('::', $submittedValues['field'], 2);
+    $configuration['field'] = $field;
+    $configuration['datasource'] = $datasource;
+    return $configuration;
+  }
+
+  /**
+   * Returns all possible fields
+   *
+   * @param $data_processor_id
+   *
+   * @return array
+   * @throws \Exception
+   */
+  protected function getFieldOptions($data_processor_id) {
+    $fieldSelect = \CRM_Dataprocessor_Utils_DataSourceFields::getAvailableFieldsInDataSources($data_processor_id, array($this, 'isFieldValid'));
+    return $fieldSelect;
+  }
+
+
+}
diff --git a/de.systopia.civiproxy/civiproxy.php b/de.systopia.civiproxy/civiproxy.php
index 109705c..bd987ad 100644
--- a/de.systopia.civiproxy/civiproxy.php
+++ b/de.systopia.civiproxy/civiproxy.php
@@ -10,6 +10,8 @@
 
 require_once 'civiproxy.civix.php';
 
+use \Symfony\Component\DependencyInjection\ContainerBuilder;
+
 /**
  * We will provide our own Mailer (wrapping the original one).
  * so we can mend all the URLs in outgoing emails
@@ -18,6 +20,15 @@ function civiproxy_civicrm_alterMailer(&$mailer, $driver, $params) {
   $mailer = new CRM_Civiproxy_Mailer($mailer);
 }
 
+/**
+ * Implements hook_civicrm_container()
+ *
+ * @link https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_container/
+ */
+function civiproxy_civicrm_container(ContainerBuilder $container) {
+  $container->addCompilerPass(new Civi\CiviProxy\CompilerPass());
+}
+
 /**
  * Implementation of hook_civicrm_config
  */
diff --git a/de.systopia.civiproxy/info.xml b/de.systopia.civiproxy/info.xml
index dba1cc6..bfe6997 100644
--- a/de.systopia.civiproxy/info.xml
+++ b/de.systopia.civiproxy/info.xml
@@ -24,4 +24,7 @@
   <civix>
     <namespace>CRM/Civiproxy</namespace>
   </civix>
+  <classloader>
+    <psr4 prefix="Civi\" path="Civi" />
+  </classloader>
 </extension>
diff --git a/docs/configuration.md b/docs/configuration.md
index a2fe7c5..389705a 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -50,7 +50,7 @@ First thing you need to configure is the base URL of your CiviProxy server using
 ```
 
 !!! note
-    This guide assumes a Drupal7 target CiviCRM with clean URLs enabled. If this is not the case for you, you might have to adjust the URLs and/or encounter issues. If so, please report on GitHub! 
+    This guide assumes a Drupal7 target CiviCRM with clean URLs enabled. If this is not the case for you, you might have to adjust the URLs and/or encounter issues. If so, please report on GitHub!
 
 ### Configuring the link to the secure target CiviCRM
 
@@ -75,12 +75,16 @@ $target_open      = $target_civicrm . '/civicrm/mailing/url/open.php';
 ```
 If you set it to the value NULL this functionality will not be available on your CiviProxy server.
 ### Setting for the location of images and included files in your mail(ing)
-CiviCRM stores images and attachments you include in your (bulk) mail in a specific folder. In CiviProxy the name of this folder is stored in variable `$target_file` in the `config.php` file:
+CiviCRM stores images and attachments you include in your (bulk) mail in a specific folder. In CiviProxy the name of this folder is stored in variable `$target_static_file` in the `config.php` file:
 ```php
-$target_file      = $target_civicrm . '/sites/default/files/civicrm/persist/';
+$target_download_file      = $target_civicrm . '/civicrm/file';
+$target_static_file      = $target_civicrm . '/sites/default/files/civicrm/persist/';
 ```
 If you set it to the value NULL this functionality will not be available on your CiviProxy server.
 
+The `$target_download_file` is used for downloading files from custom file fields (or the contact image).
+The `$target_static_file` is used for downloading images in mailings.
+
 !!! note
     By default CiviProxy will cache the files so it does not have to file from CiviCRM for each individual mail that is part of a bulk mailing. The default settings can be found in the `config.php` file:
     ```php
diff --git a/proxy/config.dist.php b/proxy/config.dist.php
index 7ddeef4..b76370c 100644
--- a/proxy/config.dist.php
+++ b/proxy/config.dist.php
@@ -41,7 +41,8 @@ $target_civicrm = 'https://your.civicrm.installation.org';
 
 // default paths, override if you want. Set to NULL to disable
 $target_rest      = $target_civicrm . '/sites/all/modules/civicrm/extern/rest.php';
-$target_file      = $target_civicrm . '/sites/default/files/civicrm/persist/';
+$target_download_file = $target_civicrm . '/civicrm/file';
+$target_static_file = $target_civicrm . '/sites/default/files/civicrm/persist/';
 $target_mosaico   = NULL; // (disabled by default): $target_civicrm . '/civicrm/mosaico/img?src=';
 $target_mosaico_template_url = NULL; // (disabled by default): $target_civicrm . '/wp-content/uploads/civicrm/ext/uk.co.vedaconsulting.mosaico/packages/mosaico/templates/';
 $target_mail_view = $target_civicrm . '/civicrm/mailing/view';
diff --git a/proxy/file.php b/proxy/file.php
index 0aa72e8..d51e6d5 100644
--- a/proxy/file.php
+++ b/proxy/file.php
@@ -10,38 +10,51 @@
 require_once "config.php";
 require_once "proxy.php";
 
-// see if file caching is enabled
-if (!$target_file) civiproxy_http_error("Feature disabled", 405);
-
 // basic check
 civiproxy_security_check('file');
 
 // basic restraints
-$valid_parameters = array( 'id'   => 'string' );
+$valid_parameters = array(
+  'id'   => 'string',
+  'eid'  => 'int',
+  'fcs'  => 'string'
+);
 $parameters = civiproxy_get_parameters($valid_parameters);
 
 // check if id specified
 if (empty($parameters['id'])) civiproxy_http_error("Resource not found");
 
-// check restrictions
-if (!empty($file_cache_exclude)) {
-  foreach ($file_cache_exclude as $pattern) {
-    if (preg_match($pattern, $parameters['id'])) {
+$static_file = true;
+if (isset($parameters['eid']) && isset($parameters['fcs'])) {
+  $static_file = false;
+  // see if file caching is enabled
+  if (!$target_download_file) civiproxy_http_error("Feature disabled", 405);
+} else {
+  // see if file caching is enabled
+  if (!$target_static_file && isset($target_file)) {
+    $target_static_file = $target_file; // Backwards compatibility.
+  }
+  if (!$target_static_file) civiproxy_http_error("Feature disabled", 405);
+  // check restrictions
+  if (!empty($file_cache_exclude)) {
+    foreach ($file_cache_exclude as $pattern) {
+      if (preg_match($pattern, $parameters['id'])) {
+        civiproxy_http_error("Invalid Resource", 403);
+      }
+    }
+  }
+  if (!empty($file_cache_include)) {
+    $accept_id = FALSE;
+    foreach ($file_cache_include as $pattern) {
+      if (preg_match($pattern, $parameters['id'])) {
+        $accept_id = TRUE;
+      }
+    }
+    if (!$accept_id) {
       civiproxy_http_error("Invalid Resource", 403);
     }
   }
 }
-if (!empty($file_cache_include)) {
-  $accept_id = FALSE;
-  foreach ($file_cache_include as $pattern) {
-    if (preg_match($pattern, $parameters['id'])) {
-      $accept_id = TRUE;
-    }
-  }
-  if (!$accept_id) {
-    civiproxy_http_error("Invalid Resource", 403);
-  }
-}
 
 // load PEAR file cache
 ini_set('include_path', ini_get('include_path') . PATH_SEPARATOR . 'libs');
@@ -52,6 +65,10 @@ $file_cache = new Cache_Lite($file_cache_options);
 // look up the required resource
 $header_key = 'header&' . $parameters['id'];
 $data_key   = 'data&'   . $parameters['id'];
+if (!$static_file) {
+  $header_key .= '&eid='.$parameters['eid'];
+  $data_key .= '&eid='.$parameters['eid'];
+}
 
 $header = $file_cache->get($header_key);
 $data   = $file_cache->get($data_key);
@@ -68,7 +85,10 @@ if ($header && $data) {
 }
 
 // if we get here, we have a cache miss => load
-$url = $target_file . $parameters['id'];
+$url = $target_static_file . $parameters['id'];
+if (!$static_file) {
+  $url = $target_download_file .'?reset=1&id='.$parameters['id'].'&eid='.$parameters['eid'].'&fcs='.$parameters['fcs'];
+}
 // error_log("CACHE MISS. LOADING $url");
 
 $curlSession = curl_init();
@@ -100,12 +120,28 @@ $body    = $content[1];
 
 // extract headers
 $header_lines = explode(chr(10), $header);
+// Check whether the Content-Disposition header is available but only when it is
+// a dynamic file.
+$content_disposition_header_present = FALSE;
+foreach ($header_lines as $header_line) {
+  if (stripos($header_line, 'Content-Disposition')===0) {
+    $content_disposition_header_present = TRUE;
+  }
+}
+if (!$static_file && !$content_disposition_header_present) {
+  // check whether the content disposition header is available.
+  // If not we are dealing with an invalid file.
+  // And CiviCRM does a redirect to the login page however we
+  // dont want to expose that through CiviProxy so we will return an error message instead.
+  civiproxy_http_error("Invalid Resource", 403);
+}
 
 // store the information in the cache
 $file_cache->save(json_encode($header_lines), $header_key);
 $file_cache->save($body, $data_key);
 
 // and reply
+$content_disposition_header_present = FALSE;
 foreach ($header_lines as $header_line) {
   header($header_line);
 }
diff --git a/proxy/proxy.php b/proxy/proxy.php
index 612688b..3a8c638 100644
--- a/proxy/proxy.php
+++ b/proxy/proxy.php
@@ -96,7 +96,7 @@ function civiproxy_redirect($url_requested, $parameters) {
  *  so they will point to this proxy instead
  */
 function civiproxy_mend_URLs(&$string) {
-  global $target_rest, $target_url, $target_open, $target_file, $target_mail, $proxy_base, $target_mosaico, $target_civicrm;
+  global $target_rest, $target_url, $target_open, $target_static_file, $target_mail, $proxy_base, $target_mosaico, $target_civicrm;
 
   if ($target_rest) {
     $string = preg_replace("#{$target_rest}#", $proxy_base . '/rest.php', $string);
@@ -110,8 +110,8 @@ function civiproxy_mend_URLs(&$string) {
   if ($target_mail) {
     $string = preg_replace("#{$target_mail}#", $proxy_base . '/mail.php', $string);
   }
-  if ($target_file) {
-    $string = preg_replace("#{$target_file}#", $proxy_base . '/file.php?id=', $string);
+  if ($target_static_file) {
+    $string = preg_replace("#{$target_static_file}#", $proxy_base . '/file.php?id=', $string);
     // https://github.com/systopia/CiviProxy/issues/38
     // fix for relative
     if ($target_mosaico) {