diff --git a/app/mailboxes/in_mailbox.rb b/app/mailboxes/in_mailbox.rb
index 64c1ee5..2e0fff9 100644
--- a/app/mailboxes/in_mailbox.rb
+++ b/app/mailboxes/in_mailbox.rb
@@ -23,8 +23,13 @@ class InMailbox < ApplicationMailbox
   end
 
   def delivered_to(mail)
-    if mail.header["Delivered-To"].present?
-      mail.header["Delivered-To"].value
+    header = mail.header["Delivered-To"]
+    if header.present?
+      if header.respond_to?(:map)
+        header.map(&:value)
+      else
+        header.value
+      end
     else
       mail.to
     end