Remote server returned message detected as spam -> 550 "The mail server detected your message as spam and has prevented delivery."

Someone trying to send us emails from their Hotmail or Gmail accounts (in this case, Hotmail) is getting a bounce and the error in the subject line. gave this error:
Remote server returned message detected as spam -> 550 “The mail server detected your message as spam and has prevented delivery.”

Spam Assassin is on, with a threshold of 8 and " Move New Spam to a Separate Folder (Spam Box):" is enabled, yet we never see the emails.

In cPanel> Track Delivery - we see no emails rejected from either of the senders email addresses.

I’m fairly good at tracking down email delivery issues and I’ve analyzed the headers, but I can’t seem to figure out why the emails are being rejected, apparently at the server level (rather than being marked as spam and put into the spam folder). The sender is legit - emails sent to an address go through just fine.

Hoping to get some help/insight to fix this issue or at least come to a reasonable explanation that we can try to work with…

Hi, we block email when the spam score is above 10. Unfortunately this doesn’t get logged by cPanel. You can try whitelisting the sender to receive it anyway.

Is it possible to disable this ‘feature’? I have just had a phone call from a client who was not getting emails from one of their clients because of this. Whitelisting can be done, however rejected email looks very unprofessional and causes costly delays. It should goto the spam folder, not be rejected.

No it cannot. Every email service has a global threshold that it uses to reject emails, and needs to in order to function, otherwise the service would fall over on itself due to the weight of the inbound spam (and the inode usage on physical disks). All email services reject email - Google, Microsoft, etc. While I understand that has a different threshold, please understand that we do not have their server software. We use open source software to manage this. I understand the desire to throw the baby out with the bathwater when it’s to your attention, but keep in mind it’s been this way for over 3 years that you’ve been a customer and you’re just now dealing with a case that you’d like to review. It’s totally okay to back up for a moment and ask “Are the senders doing something wrong?” They may well be, or maybe we are, happy to look into it.

If you would like me to look into a specific rejection that you think was unfair, feel free to reach out to me at and tell me the sender, recipient, and an estimate on the date and/or subject if you can.