fix: Mailgun reply-to header and named 'to' recipient support

Author: deepshekhardas

src/Utopia/Messaging/Adapter/Email/Mailgun.php

@@ -52,7 +52,7 @@ protected function process(EmailMessage $message): array
 
         $domain = $this->isEU ? $euDomain : $usDomain;
 
-        $recipients = $message->getTo();
+$recipients = $message->getTo();
         $toEmails = \array_map(fn ($to) => $to['email'], $recipients);
 
         $body = [
@@ -66,9 +66,12 @@ protected function process(EmailMessage $message): array
             'subject' => $message->getSubject(),
             'text' => $message->isHtml() ? null : $message->getContent(),
             'html' => $message->isHtml() ? $message->getContent() : null,
-            'h:Reply-To: '."{$message->getReplyToName()} <{$message->getReplyToEmail()}>",
         ];
 
+        if (!empty($message->getReplyToEmail())) {
+            $body['h:Reply-To'] = "{$message->getReplyToName()} <{$message->getReplyToEmail()}>";
+        }
+
         if (\count($recipients) > 1) {
             $body['recipient-variables'] = json_encode(array_fill_keys($toEmails, []));
         }