Patch that adds return_path / envelope FROM to Sparkpost Drupal module

sparkpost-return_path.patch

diff --git a/config/install/sparkpost.settings.yml b/config/install/sparkpost.settings.yml
index e014059..504215a 100644
--- a/config/install/sparkpost.settings.yml
+++ b/config/install/sparkpost.settings.yml
@@ -2,6 +2,7 @@ api_key:
 debug: true
 sender:
 sender_name:
+return_path:
 format: ''
 async: false
 skip_cron: false
diff --git a/config/schema/sparkpost.schema.yml b/config/schema/sparkpost.schema.yml
index 0078d20..0e7e50e 100644
--- a/config/schema/sparkpost.schema.yml
+++ b/config/schema/sparkpost.schema.yml
@@ -14,6 +14,9 @@ sparkpost.settings:
     sender_name:
       type: text
       label: 'Sender name'
+    return_path:
+      type: text
+      label: 'Return path'
     format:
       label: 'Format to format message'
       type: text
diff --git a/src/Form/SettingsForm.php b/src/Form/SettingsForm.php
index 58e2674..4497de5 100644
--- a/src/Form/SettingsForm.php
+++ b/src/Form/SettingsForm.php
@@ -100,6 +100,12 @@ class SettingsForm extends ConfigFormBase {
         '#default_value' => $config->get('sender_name'),
         '#description' => $this->t('Optionally enter a from name to be used.'),
       ];
+      $form['options']['return_path'] = [
+        '#type' => 'textfield',
+        '#title' => $this->t('Return path'),
+        '#default_value' => $config->get('return_path'),
+        '#description' => $this->t('Optionally enter an email address to use for envelope FROM.')
+      ];
       $options = ['' => $this->t('-- Select --')];
       $formats = filter_formats();
       foreach ($formats as $key => $format) {
@@ -146,6 +152,7 @@ class SettingsForm extends ConfigFormBase {
       ->set('debug', $form_state->getValue('debug'))
       ->set('sender_name', $form_state->getValue('sender_name'))
       ->set('sender', $form_state->getValue('sender'))
+      ->set('return_path', $form_state->getValue('return_path'))
       ->set('format', $form_state->getValue('format'))
       ->set('async', $form_state->getValue('async'))
       ->set('skip_cron', $form_state->getValue('skip_cron'))
diff --git a/src/Plugin/Mail/SparkpostMail.php b/src/Plugin/Mail/SparkpostMail.php
index 455d4bf..718c741 100644
--- a/src/Plugin/Mail/SparkpostMail.php
+++ b/src/Plugin/Mail/SparkpostMail.php
@@ -124,6 +124,7 @@ class SparkpostMail implements MailInterface {
         'options' => [
           'transactional' => TRUE,
         ],
+        'return_path' => $this->config->get('return_path')
       ];
 
       // @todo: Handle response in some way.