small fix

Author: francescobianco

src/BodyStructure.php

@@ -308,7 +308,7 @@ protected static function processSubPartAsMessage($item)
         ];
 
         foreach ($item[8] as $itemPart) {
-            if ($itemPart[2] == 'ALTERNATIVE') {
+            if (isset($itemPart[2]) && $itemPart[2] == 'ALTERNATIVE') {
                 $message->parts[] = self::extractPartAsAlternative($itemPart);
                 continue;
             }

src/Functions.php

@@ -30,7 +30,7 @@ public static function getHostFromMailbox($mailbox)
     {
         $mailboxParts = is_array($mailbox) ? $mailbox : self::parseMailboxString($mailbox);
 
-        return $mailboxParts['host'];
+        return @$mailboxParts['host'];
     }
 
     public static function getSslModeFromMailbox($mailbox)

src/HeaderInfo.php

@@ -93,7 +93,7 @@ protected static function parseAddressList($address, $defaultHost)
         foreach ($addressList as $objectEntry) {
             $addressEntry = (object) [
                 'personal' => $objectEntry->personal ?? null,
-                'mailbox' => $objectEntry->mailbox,
+                'mailbox' => @$objectEntry->mailbox,
                 'host' => @$objectEntry->host,
             ];