Large messages now have “X-Spam-known-sender” header added

After a recent upgrade to our email delivery system, there was a bug where large messages (>500k) would never have the “X-Spam-known-sender” header added, even if the From address of the email was a known sender. This was affecting a small number of users who use “White list only” spam protection level and were receiving emails with large attachments. This has now been fixed.