552 Spam Message Rejected 221 avasin[0-9][0-9].plus.net Plusnet Cloudmark Gateway

[#1]

When our company's system sends to a plusnet address we often see the response in the Subject of this Post.

Cloudmark ( https://csi.cloudmark.com/en/reset ) say for our mail server address:

Submitted IP Address is Not Listed in Cloudmark Sender Intelligence

The SMTP rejection that you have received is not the result of current data provided by Cloudmark Sender Intelligence.

Can you help us get these legitmate mails to our (and plusnet's) customers?

[#2]

Hello? Anyone there? For some similar posts admins offered to assist via private messaging but I don't know how to send such a private message to an admin...

These mails are definitely legitimate but we continue to see (some details replaced by ...)

QUIT250 <...> sender ok
250 <jeremy@...plus.com> recipient ok
354 OK
552 Spam Message Rejected

221 avasin10.plus.net Plusnet Cloudmark Gateway closing connection

And Cloudmark continue to deny our IP is listed.

[#3]

Following some back and forth with Cloudmark Customer support they have said:

Hello Jeremy,

The sample you are providing tests as legit. As does the IP you previously show.

You need to contact Plusnet to identify why they are rejecting your message, they will have local logs to exactly identify the reason. If its agreed this is a false positive they can use the tools we provide to remediate or escalate to the Proofpoint Support team

In this case there is insufficient evidence for us to give a reason for problem - this may not even be a Cloudmark Authority issue given or tests are not giving a spam verdict.

Please can you direct me to the correct route to get this looked at?

[#4]

Following further testing and analysis, it appears that Plusnet email servers reject a dash character which under certain circumstances appears as  "~@~S" (eg, WSL SSH + vi ) but in most circumstances (eg, Windows Notepad, iTerm2 SSH + vi) appears just as a dash... ...I am asking developers if their email templates might be modified but it is notable that many other mail servers on the internet we have worked with are not rejecting this, and I suspect Plusnet email servers might be outdated in their handling of newer character codes.

[#5]

I have received the attached email headers in the past 24 hours.

They are Spam emails which attempt to trick / blackmail the user to pay a Bitcoin ransom.

To me these vile messages should be being blocked by Plus Net.

This is the content of one of them:-

Hello!
Have you recently noticed that I have e-mailed you from your account?
Yes, this simply means that I have total access to your device.

For the last couple of months, I have been watching you.
Still wondering how is that possible? Well, you have been infected with malware originating from an adult website that you visited. You may not be familiar with this, but I will try explaining it to you.

With help of the Trojan Virus, I have complete access to a PC or any other device.
This simply means I can see you at any time I wish to on your screen by simply turning on your camera and microphone, without you even noticing it. In addition, I have also got access to your contacts list and all your correspondence.

You may be asking yourself, "But my PC has an active antivirus, how is this even possible? Why didn't I receive any notification?" Well, the answer is simple: my malware uses drivers, where I update the signatures every four hours, making it undetectable, and hence keeping your antivirus silent.

I have a video of you [-Censored-] on the left screen, and on the right screen - the video you were watching while masturbating.
Wondering how bad could this get? With just a single click of my mouse, this video can be sent to all your social networks, and e-mail contacts.
I can also share access to all your e-mail correspondence and messengers that you use.

All you have to do to prevent this from happening is - transfer bitcoins worth $1450 (USD) to my Bitcoin address (if you have no idea how to do this, you can open your browser and simply search: "Buy Bitcoin").

My bitcoin address (BTC Wallet) is: 1AbhXaiFxR52NDTrjAtzsdyhooVNoVchy1

After receiving a confirmation of your payment, I will delete the video right away, and that's it, you will never hear from me again.
You have 2 days (48 hours) to complete this transaction.
Once you open this e-mail, I will receive a notification, and my timer will start ticking.

Any attempt to file a complaint will not result in anything, since this e-mail cannot be traced back, same as my bitcoin id.
I have been working on this for a very long time by now; I do not give any chance for a mistake.

If, by any chance I find out that you have shared this message with anybody else, I will broadcast your video as mentioned above.