Emails from and to a particular sender being blocked

[#1]

Hi, I'm a new member and have looked for similar issues on here but can't see anything that fits the bill exactly.  Apologies if I've missed something.

I received order confirmation emails from a supplier in March but for an order a couple of days ago their system is having emails to me rejected.  I don't have their error message I'm afraid.

I found this out as I emailed them yesterday morning to ask why I hadn't heard from them and they rang me to say what the problem was.  At their suggestion I added them to my Safe Senders list and emailed them (or tried to) to confirm this.  The email was rejected as undeliverable with this message (email addresses anonymised):

        The following recipient(s) cannot be reached:

        'xxxxx@xxxxxxx-xxxxx.co.uk' on 10/07/2020 06:35
        552 tlgujOFVdjUVQtlgvjFF2n message rejected due to spam or virus. If you believe this is in error please login to your            portal or contact your ISP support team.

        'yyy@xxxxxxx-xxxxx.co.uk' on 10/07/2020 06:35
        552 tlgujOFVdjUVQtlgvjFF2n message rejected due to spam or virus. If you believe this is in error please login to your            portal or contact your ISP support team.

I tried adding the addresses to my Safe Recipients list and emailing again but the same thing happened.

I'm sending and receiving emails from/to other people without problem.  It's puzzling that they could email me OK in March but not now, and that I was able to send an email to one of these addresses in the morning but not later that day. 

Can anyone help please?

[#2]

Hi @LJD 

A warm welcome to the forums.

With the level of sanitisation you've performed, there is nothing the community can really do to assist you.  Without the target domain, it is not possible to undertake any testing in an attempt to reproduce the error.  I would suspect that teh sender's domain has become suspected of being a source of spam.

A staff member might be able to find the relevant message from the system logs using the 552 error finger print you've posted.

@JW are you able to assist please?

[#3]

I've had someone with the relevant access take a look at the logs. They can see the rejection you received this morning, though checking the rejection string again now shows that it's already been reset by the wider Cloudmark community. So if you attempt to send the email again now it should go without further issues.