DU6PEPF0000B621.mail.protection.outlook.com rejected your message

Question

Several people in my network tell me that they receive an Outlook rejection notification when they email me.

The notifications are similar and say:

DU6PEPF0000B621.mail.protection.outlook.com rejected your message to the following email addresses: [...]

Your message wasn't delivered because the recipient's email provider rejected it.

Even if I received their messages.

I checked and I do not have any rules in my Outlook profile.

Does anyone know how I can fix this issues?

Thanks a lot, Lucio

Answer 1

Hi Noel, any more thoughts/suggestions on my issue?

Since it is several senders (from different domains) who receive a "reject" notification from my Hotmail, I don't think the problem is on their side.

I listed their domains in my "safe domains" list, but this did not change the outcome (in fact, the safe list is about what goes in the junk folder, my problem is different... I seem to regularly receive their emails in my inbox, but they receive a rejection notification).

Like I said, I do not have any rules in my account.

I need to solve this issue because it may alienate my senders... Thanks a lot for your help, Lucio

Answer 2

Hi,

Thank you for sharing your question. I understand how confusing and concerning it is when people attempting to reach you get ‘message rejected’ errors even though the messages still arrive in your inbox. This situation often happens when Outlook.com or Microsoft 365 briefly flags a sender’s domain, IP address, or authentication status during the delivery process, causing the system to generate a bounce notification even though the message is later accepted on retry. It can also occur when filtering rules, throttling limits, or anti‑spam protections temporarily reject part of a message flow before the message is eventually delivered to your mailbox.

To resolve this, you can check your Outlook Junk Email settings and Safe Senders list to ensure none of the affected addresses are being filtered incorrectly, verify whether any external forwarding, aliases, or connected accounts could be causing mixed delivery paths, and review your mailbox status on Outlook.com to confirm the account is fully active. If the issue continues, sharing the rejection details with the senders’ mail administrators can help confirm whether their domain has authentication issues such as SPF, DKIM, or DMARC failures that occasionally trigger Microsoft’s filtering system. Although you do not have rules in your profile, mailbox-level security or remote filters can still generate these errors until the sender’s domain reputation stabilizes.

Before we look into deeper options, may I ask whether all senders experience this issue or only people from specific domains or companies? I’m here to help you resolve this fully, so feel free to follow up with any additional bounce message details and we can move to the next steps together.”

 

I hope this helps.

Best Regards,

Noel