Starting emails with "BEGIN PGP MESSAGE" will fool the filter

I remember annoying friends in a mailing list by quoting emails with "begin quote from Person Name:" :)

Fewer, but some, inspect files to deduce their type.

None care about encrypted zips with the file renamed to a common extension (encrypted zip manifests are unencrypted, so the file names are still visible).

I can imagine some reasons why it would work better than merely checking the URLs when filtering: not rewriting but simply checking and scoring against other spam rules. But also see reasons why it secures less well.

Pro: you can block URLs post-delivery. E.g. an advisary changes the link to malware or phishing after some time/n requests/based on user agent. Con: all encryption, including DKIM, GPG etc break.

Edit: to clarify why I don't understand why this works: and advisary can still do the same: i.e. serve an innocent page to the checker but then a bad webpage to the actual visitor. Not trivial, but not hard either.

A good middle ground might be to scan URLs on the mailserver against lists and maybe open the page and scan its content before delivering. Then have the client intercept links and redirect them through another on-demand checker?

Because obviously, training people to "not click links in emails" or use only plain text or both, hasn't worked in the last decades.

<meta content='Our university deployed a mail filter that rewrites URLs in emails to redirect them via a service that checks for bad websites. Somebody clever worked out that PGP-signed emails are exempt from the rewrite rule, so now people are starting their emails with &quot;BEGIN PGP MESSAGE&quot; even though they haven&#39;t used PGP at all, just to fool the filter

Anybody sending malware links has probably also worked out that trick by now, thereby rendering the entire filter pointless' name='description'>

Now I'm thinking if there was some smart idea behind that trying to fool some filters.

----- BEGIN EDIT -----

I can see it from the mastadon app but not in browser. I took a screenshot for others: https://i.imgur.com/q3DA7wQ.png

Text is:

  Our university deployed a mail filter that rewrites URLs in emails to redirect them via a service that checks for bad websites. Somebody clever worked out that PGP-signed emails are exempt from the rewrite rule, so now people are starting their emails with "BEGIN PGP MESSAGE" even though they haven't used PGP at all, just to fool the filter 

  Anybody sending malware links has probably also worked out that trick by now, thereby rendering the entire filter pointless

----- END EDIT -----

But I have an interesting issue which is (presumably) related. I keep getting obviously spam emails in my gmail and Google has refused to do anything about it (after finally getting through to support). These are embarrassingly bad emails. Ones you'd expect a naive bayesian classifier to get near 100% accuracy on!

In the "to" address is something that's not even remotely my email. Suppose I'm godelski@gmail.com, the "to" has something like "robbert01@gmail.com" and always has a CC with a different number. Subject lines will be things like "confirmation of receipt" but in non-standard and inconsistent fonts. And the message body is that all too typical single image and claim of something like winning a home depot gift card. The "from" address is always some scammy looking address. So Naive Bayes should get it on just this alone!

But the weird thing is when you show the original message. There's PAGES of stuff in here (about 20 pages or 9.5k words)! All kinds of email conversations, things including stuff like "here is your one time <account> password", stuff in other languages, survey questions, conversations, and a lot more. I actually did a diff on a few of these and they're almost identical too! I can't help but think that these are some weird prompt injections. It looks like it is written by a madman, but it it's probably some "throw shit at the wall and see what sticks" kinda thing.

But the message ID always comes from some Microsoft (something like microsoftstore1.microsoft.com). This is where Google support said it isn't their problem and moved on. I'm pretty critical of LLMs and their ability to reason, but I feel often we're trying to turn humans into machines instead of letting them complement one another. And I think this is why so many business people like LLMs, because they think everything can be figured out with clear immutable rules. But the thing is that the environment always changes and you need something that's not only adaptable, but can reason AND understands the actual desired outcome that humans want.

I hope someone at Google pays attention. Because you can't just hand all thinking over to humans. We're not there yet and it's why everything is going to shit (not just Google)