mschudders
--- a/src/Plugin/MailerTransport/TransportBase.php
+++ b/src/Plugin/MailerTransport/TransportBase.php
   */
  public function getDsn() {
    $cfg = $this->configuration;
-    $query = !empty($cfg['query']) ? array_filter($cfg['query']) : [];
+    // Cannot do array_filter because this will filter out 0 params values.
+    // Which you want to disable verification for example.
+    $query = !empty($cfg['query']) ? $cfg['query'] : [];
--- a/symfony_mailer.install
+++ b/symfony_mailer.install
 use Drupal\filter\Entity\FilterFormat;
 use Drupal\symfony_mailer\Entity\MailerPolicy;
 use Drupal\symfony_mailer\Entity\MailerTransport;
+use Drupal\symfony_mailer\Plugin\MailerTransport\SmtpTransport;
--- a/config/schema/symfony_mailer.schema.yml
+++ b/config/schema/symfony_mailer.schema.yml
+      mapping:
+        local_domain:
+          type: string
+          label: 'HELO command domain name'
+        ping_threshold:
+          type: integer
+          label: 'Ping threshold'
+        restart_threshold:
+          type: integer
+          label: 'Restart threshold'
+        restart_threshold_sleep:
+          type: integer
+          label: 'Restart threshold sleep'
+        verify_peer:
+          type: boolean
+          label: 'Verify peer'
--- a/src/Plugin/MailerTransport/SmtpTransport.php
+++ b/src/Plugin/MailerTransport/SmtpTransport.php
      '#max' => 65535,
    ];

+    $form['query']['verify_peer'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('TLS Peer Verification'),
+      '#description' => $this->t('It is not recommended to disable peer verification for security reasons, it can be useful while developing or when using a self-signed certificate.'),