Add mailers config

Author: Iaotle

config/dkim.php

@@ -9,4 +9,5 @@
     'passphrase' => env('DKIM_PASSPHRASE', ''),
     'algorithm' => env('DKIM_ALGORITHM', 'rsa-sha256'),
     'identity' => env('DKIM_IDENTITY', null),
+    'mailers' => env('DKIM_MAILERS', ['smtp', 'sendmail', 'log', 'mail']),
 ];

src/Mailer.php

@@ -57,7 +57,8 @@ public function send($view, array $data = [], $callback = null): ?SentMessage
         $privateKey = config('dkim.private_key');
         $selector = config('dkim.selector');
         $domain = config('dkim.domain');
-        if (in_array(strtolower(config('mail.default')), ['smtp', 'sendmail', 'log', 'mail'])) {
+        $mailers = config('dkim.mailers');
+        if (in_array(strtolower(config('mail.default')), $mailers, true)) {
             if (empty($privateKey)) {
                 throw new InvalidArgumentException('No private key set.', 1588115551);
             }