Issues with certain email addresses

Question

Issues with certain email addresses

Victorine Lambert 5

Hi,

I am not receiving emails sent from @cnrs.fr addresses to my Hotmail/Outlook.com address. The messages do not appear in Junk Email or any other folder. I am on a Mac if that helps but I don't think it's the issue. What could you suggest because these emails are very important.

Could I check whether there is a mail delivery/filtering issue between the CNRS mail servers and Microsoft Outlook.com?

Thanks,

Victorine

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2 answers

Your answer

Answer 1

Victorine Lambert 5

It does not bounce back. People do not get an email saying they cannot send it to my email address.

Jeronimo Fuerte 45,485 Reputation points Independent Advisor

2026-08-25T17:24:51.7433333+00:00

The absence of a bounce-back does not prove that Microsoft received the messages. The definitive check must be performed by the CNRS mail administrator using the outbound SMTP logs or message trace. They should search using the exact sender, recipient, sending time, and Message-ID, then identify Microsoft’s final SMTP response. A 250 response means Microsoft accepted the message; a temporary deferral, rejection, or no connection indicates that delivery stopped before it reached the Outlook.com mailbox. Message tracing requires administrator access and cannot be performed by an Outlook.com user.

If the CNRS server shows a rejection or deferral, its administrator must review its SPF, reverse DNS and sending-IP reputation and submit the case through Outlook.com Sender Support; adding the domain as a safe sender cannot override a rejection that occurs before the message reaches the mailbox.

Answer 2

If messages from @cnrs.fr never appear in Inbox, Junk Email, or any other folder, the most likely causes are either Outlook.com filtering/settings on the mailbox or the sender domain being rejected before delivery.

Suggested checks in Outlook.com:

Check the Other tab if Focused Inbox is enabled.
Check the Junk Email folder and Junk Email settings.
Check whether email forwarding is enabled.
Check whether any rules are moving or deleting the messages.
Add the sender address or cnrs.fr domain to Safe senders and domains:
- Settings > Mail > Junk email
- Under Safe senders and domains, select Add safe sender and add the address or domain, then Save.

Important limitation: if Outlook.com is blocking the message before it reaches the mailbox, adding a safe sender may not help. In that case, the sender needs to check whether they receive a bounce-back/non-delivery report.

What to ask the CNRS sender to verify:

Send a test message to the Outlook.com address.
Check whether they receive a non-delivery report or bounce-back.
If they do, review the exact error text. Microsoft guidance in similar cases indicates the sender may need to correct their email authentication settings, especially SPF-related issues, or use a different sending address temporarily.

About checking whether this is a delivery/filtering issue between CNRS and Microsoft:

Yes — the practical way to confirm that is from the sender side by checking for a bounce-back/non-delivery report after sending a test email. If there is no message in Inbox, Junk, Other, or another folder, and no forwarding/rule explains it, that strongly suggests the message may be blocked before it reaches the mailbox.

Since the issue is with Outlook.com delivery, being on a Mac is not likely the main factor here.