GyazMail & "undeliverable" spam

I’ve been using SpamSieve for a while now with GyazMail, and thought I had things pretty well trained and tuned. Over the last few days, I have been absolutely swamped with spam purporting to be bounce messages (you know the sort, “Undeliverable mail”, or “Delivery Status Notification”), and SpamSieve is letting over half of these through. This kind of spam is certainly not new, and I’ve always received some amount of it, but the volume has seriously increased, and for some reason, SpamSieve is now letting most of it through.

Even worse, I’ve been dutifully marking every one of them as Junk by choosing Message --> Junk --> Mark as Junk in GyazMail, but it doesn’t seem as if SpamSieve is getting any better at recognizing these spams!

What can I do? Is there a way to tweak settings to improve the performance?

Please see this page.