diff --git a/VERSION.txt b/VERSION.txt
index 184f305de134..9a532528f270 100644
--- a/VERSION.txt
+++ b/VERSION.txt
@@ -1 +1 @@
-5.5.10
\ No newline at end of file
+5.5.11
\ No newline at end of file
diff --git a/app/Jobs/Mail/NinjaMailerJob.php b/app/Jobs/Mail/NinjaMailerJob.php
index 598156ce711a..b157176b027c 100644
--- a/app/Jobs/Mail/NinjaMailerJob.php
+++ b/app/Jobs/Mail/NinjaMailerJob.php
@@ -102,6 +102,17 @@ class NinjaMailerJob implements ShouldQueue
 
         $this->nmo->mailable->tag($this->company->company_key);
 
+        if($this->nmo->invitation)
+        {
+
+            $this->nmo
+                 ->mailable
+                 ->withSymfonyMessage(function ($message) {
+                    $message->getHeaders()->addTextHeader('x-invitation', $this->nmo->invitation->key);     
+                 });
+
+        }
+
         //send email
         try {
             nlog("trying to send to {$this->nmo->to_user->email} ". now()->toDateTimeString());
diff --git a/app/Jobs/PostMark/ProcessPostmarkWebhook.php b/app/Jobs/PostMark/ProcessPostmarkWebhook.php
index 64b590ad0917..0dca3f00e727 100644
--- a/app/Jobs/PostMark/ProcessPostmarkWebhook.php
+++ b/app/Jobs/PostMark/ProcessPostmarkWebhook.php
@@ -26,6 +26,7 @@ use App\Models\Company;
 use App\Models\CreditInvitation;
 use App\Models\InvoiceInvitation;
 use App\Models\Payment;
+use App\Models\PurchaseOrderInvitation;
 use App\Models\QuoteInvitation;
 use App\Models\RecurringInvoiceInvitation;
 use App\Models\SystemLog;
@@ -283,6 +284,8 @@ class ProcessPostmarkWebhook implements ShouldQueue
             return $invitation;
         elseif($invitation = CreditInvitation::where('message_id', $message_id)->first())
             return $invitation;
+        elseif($invitation = PurchaseOrderInvitation::where('message_id', $message_id)->first())
+            return $invitation;
         else
             return $invitation;
     }
diff --git a/app/Listeners/Mail/MailSentListener.php b/app/Listeners/Mail/MailSentListener.php
index 7d52131bb551..e1a620c0e770 100644
--- a/app/Listeners/Mail/MailSentListener.php
+++ b/app/Listeners/Mail/MailSentListener.php
@@ -12,9 +12,15 @@
 namespace App\Listeners\Mail;
 
 use App\Libraries\MultiDB;
+use App\Models\CreditInvitation;
+use App\Models\InvoiceInvitation;
+use App\Models\PurchaseOrderInvitation;
+use App\Models\QuoteInvitation;
+use App\Models\RecurringInvoiceInvitation;
 use Illuminate\Contracts\Queue\ShouldQueue;
 use Illuminate\Mail\Events\MessageSent;
 use Illuminate\Support\Facades\Notification;
+use Symfony\Component\Mime\MessageConverter;
 
 class MailSentListener implements ShouldQueue
 {
@@ -35,19 +41,50 @@ class MailSentListener implements ShouldQueue
      */
     public function handle(MessageSent $event)
     {
-        nlog("mail listener");
-        nlog($event);
-        // if (property_exists($event->message, 'invitation') && $event->message->invitation) {
-        //     MultiDB::setDb($event->sent->invitation->company->db);
 
-        //     if ($event->message->getHeaders()->get('x-pm-message-id')) {
-        //         $postmark_id = $event->sent->getHeaders()->get('x-pm-message-id')->getValue();
+        $message_id = $event->sent->getMessageId();
+
+        $message = MessageConverter::toEmail($event->sent->getOriginalMessage());
+
+        $invitation_key = $message->getHeaders()->get('x-invitation')->getValue();
+
+        if($message_id && $invitation_key)
+        {
+
+            $invitation = $this->discoverInvitation($invitation_key);
+
+            if(!$invitation)
+                return;
+
+            $invitation->message_id = $message_id;
+            $invitation->save();   
+        }
 
-        //         // nlog($postmark_id);
-        //         $invitation = $event->sent->invitation;
-        //         $invitation->message_id = $postmark_id;
-        //         $invitation->save();
-        //     }
-        // }
     }
+
+    private function discoverInvitation($key)
+    {
+        
+        $invitation = false;
+
+        foreach (MultiDB::$dbs as $db) 
+        {
+
+            if($invitation = InvoiceInvitation::on($db)->where('key', $key)->first())
+                return $invitation;
+            elseif($invitation = QuoteInvitation::on($db)->where('key', $key)->first())
+                return $invitation;
+            elseif($invitation = RecurringInvoiceInvitation::on($db)->where('key', $key)->first())
+                return $invitation;
+            elseif($invitation = CreditInvitation::on($db)->where('key', $key)->first())
+                return $invitation;
+            elseif($invitation = PurchaseOrderInvitation::on($db)->where('key', $key)->first())
+                return $invitation;
+
+        }
+
+        return $invitation;
+
+    }
+
 }
diff --git a/app/Providers/EventServiceProvider.php b/app/Providers/EventServiceProvider.php
index 495ebf41aadd..53bb69bbb4ca 100644
--- a/app/Providers/EventServiceProvider.php
+++ b/app/Providers/EventServiceProvider.php
@@ -271,9 +271,9 @@ class EventServiceProvider extends ServiceProvider
         ],
         MessageSending::class => [
         ],
-        // MessageSent::class => [
-        //     MailSentListener::class,
-        // ],
+        MessageSent::class => [
+            MailSentListener::class,
+        ],
         UserWasCreated::class => [
             CreatedUserActivity::class,
             SendVerificationNotification::class,
diff --git a/config/ninja.php b/config/ninja.php
index 7db45a89e570..286bbdc05d9f 100644
--- a/config/ninja.php
+++ b/config/ninja.php
@@ -14,8 +14,8 @@ return [
     'require_https' => env('REQUIRE_HTTPS', true),
     'app_url' => rtrim(env('APP_URL', ''), '/'),
     'app_domain' => env('APP_DOMAIN', 'invoicing.co'),
-    'app_version' => '5.5.10',
-    'app_tag' => '5.5.10',
+    'app_version' => '5.5.11',
+    'app_tag' => '5.5.11',
     'minimum_client_version' => '5.0.16',
     'terms_version' => '1.0.1',
     'api_secret' => env('API_SECRET', ''),