Allow to add custom headers to outgoing emails via APP_CUSTOM_MAIL_HEADERS env variable - closes #2546

.env.example

@@ -19,6 +19,9 @@ APP_URL=https://example.com
 # (access to freescout.net is required to obtain official modules)
 #APP_PROXY=
 
+# Custom headers to add to all outgoing emails.
+#APP_CUSTOM_MAIL_HEADERS="IsTransactional:True;X-Custom-Header:value"
+
 # Timezones: https://github.com/freescout-helpdesk/freescout/wiki/PHP-Timezones
 # Comment it to use default timezone from php.ini
 #APP_TIMEZONE=Europe/London

app/Mail/Alert.php

@@ -32,6 +32,8 @@ class Alert extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         $subject = '['.\Config::get('app.name').'] ';
         if (!empty($this->title)) {
             $subject .= $this->title;

app/Mail/AutoReply.php

@@ -44,6 +44,8 @@ class AutoReply extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         $view_params = [];
 
         // Set headers

app/Mail/PasswordChanged.php

@@ -26,6 +26,8 @@ class PasswordChanged extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         $message = $this->subject(__('Password Changed'))
                     ->view('emails/user/password_changed')
                     ->text('emails/user/password_changed_text');

app/Mail/ReplyToCustomer.php

@@ -64,6 +64,8 @@ class ReplyToCustomer extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+
         // Set Message-ID
         // Settings via $this->addCustomHeaders does not work
         $new_headers = $this->headers;

app/Mail/Test.php

@@ -23,6 +23,8 @@ class Test extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         $this->withSwiftMessage(function ($swiftmessage) {
             $headers = $swiftmessage->getHeaders();
             $headers->addTextHeader('X-FreeScout-Mail-Type', 'test.mailbox');

app/Mail/UserEmailReplyError.php

@@ -25,6 +25,8 @@ class UserEmailReplyError extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         return $this->subject(__('Unable to process your update'))
             ->view('emails/user/email_reply_error');
     }

app/Mail/UserInvite.php

@@ -27,6 +27,8 @@ class UserInvite extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         $message = $this->subject(__('Welcome to :company_name!', ['company_name' => Option::getCompanyName()]))
                     ->view('emails/user/user_invite')
                     ->text('emails/user/user_invite_text');

app/Mail/UserNotification.php

@@ -70,6 +70,8 @@ class UserNotification extends Mailable
      */
     public function build()
     {
+        \MailHelper::prepareMailable($this);
+        
         // Set Message-ID
         // Settings via $this->addCustomHeaders does not work
         $new_headers = $this->headers;

app/Misc/Mail.php

@@ -806,6 +806,32 @@ class Mail
         }
     }
 
+    public static function prepareMailable($mailable)
+    {
+        $custom_headers_str = config('app.custom_mail_headers');
+
+        if (empty($custom_headers_str)) {
+            return;
+        }
+
+        $custom_headers = explode(';', $custom_headers_str);
+
+        $mailable->withSwiftMessage(function ($swiftmessage) use ($custom_headers) {
+            $headers = $swiftmessage->getHeaders();
+
+            foreach ($custom_headers as $custom_header) {
+                $header_parts = explode(':', $custom_header);
+
+                $header_name = trim($header_parts[0] ?? '');
+                $header_value = trim($header_parts[1] ?? '');
+                if ($header_name && $header_value) {
+                    $headers->addTextHeader($header_name, $header_value);
+                }
+            }
+            return $swiftmessage;
+        });
+    }
+
     // public static function oauthGetProvider($provider_code, $params)
     // {
     //     $provider = null;

config/app.php

@@ -366,6 +366,14 @@ return [
     */
     'proxy' => env('APP_PROXY', ''),
 
+    /*
+    |--------------------------------------------------------------------------
+    | Custom headers to add to all outgoing emails.
+    | https://github.com/freescout-helpdesk/freescout/issues/2546#issuecomment-1380414908
+    |--------------------------------------------------------------------------
+    */
+    'custom_mail_headers' => env('APP_CUSTOM_MAIL_HEADERS', ''),
+
     /*
     |--------------------------------------------------------------------------
     | Autoloaded Service Providers