550 5.7.350 Remote server returned message detected as spam

Question

I have emails that don't want to reach the recipient, but I can't determine whether the problem is with them or with me?

550 5.7.350 Remote server returned message detected as spam -> 554 5.7.1 Message refused by SURBL check. m**i.s****.ch This email from IP 5*.*.*.0 has been rejected. The email message was detected as spam.

En-têtes du message d’origine

(The message header has been moved to private message)

Answer 1

Hello Thomas Kisszalay ADM**,**

Good day!! Thank you for reaching out to Microsoft community.

Based on the provided description, it seems that the email you are trying to send has been detected as spam by the recipient's email server, leading to the 550 5.7.350 error. This could be due to various reasons such as the content of the email, the sender's email address, or the email server's reputation.

Since we do not have additional information regarding your issue, we cannot say for certain which is causing this issue for the moment. As you know in Mail flow there could be a number of possibilities for marked as SPAM. But here are some steps you can take for future incidents for a healthy Mail flow.

Follow this article for more information: Fix NDR error 550 5.7.1 in Exchange Online - Exchange | Microsoft Learn.

• The sender is external, and their source IP address is on Microsoft's blocklist.
• Your domain's MX record might have problem.
• Your domain's MX record might have problem.
• If your domain isn't fully enrolled in Microsoft 365 or Office 365, try the following steps:
  • Verify your domain appears as Healthy in the Microsoft 365 admin center at Settings > Domains.

To resolve this issue, you can try the following initial steps:

• You can ask the recipient to whitelist your IP address.
• My suggestion is to add the sender’s domain in the safe sender list and allow list in the spam filter.
• Check the content of your email and ensure that it does not contain any spammy or suspicious content.
• Contact the recipient and ask them to check their spam or junk folder to see if your email has been mistakenly marked as spam.
• Depending on the recipient side and if you have access to the Exchange admin center, we can add a connector to force outgoing traffic to recipient mail hosts to use IPv4 apparently fixed the issue (Mostly on google service provider).

Additionally, I have checked your domain reputation also the header you have sent, it's strange to admit that there should be a reason for marking your email as SPAM. your domain reputation seems fine also the message header SCL value seems fine along with other data.

So, we looked into the service incident, and this is what we found below:

• Title: Users are unable to receive email messages from external domains within Exchange Online
• User impact: Users are unable to receive email messages from external domains within Exchange Online.
• Current status: We’re continuing to review details provided in the support case and are attempting to retrieve diagnostic data from our telemetry to identify the source of the issue and formulate a mitigation plan.
• Scope of impact: Your organization is affected by this event, and any user attempting to receive email messages from external domains is impacted.

I hope this helps. Let me know if you have any further questions or concerns.

To better understand the issue and after the Serice Incident is lifted, if you still experience the same issue, I need your help on sending all the answers along with the data only via Private Messages - Microsoft Community. So that we can get on the same page and resolve the issue together:

• What about sending emails to other users within the organization, does this issue happen too?
• May I know your affected account type and subscription? Is it Microsoft365 business or Microsoft Personal account (outlook.com/Hotmail.com/live.com) or any third-party account?
• Could you please provide us product and version details of your Outlook? About Office: What version of Office am I using? - Microsoft Support and What version of Outlook do I have? - Microsoft Support.
• At the recipient side, which service provider are they using?
• When this issue started to occur?
• Was it working normally before?
• If it was working initially? On that case, may I know have you make any recent changes on your Outlook/device/account/permission/update office, etc.?
• Are you a global administrator user or an End user?
• Do you have access to Microsoft 365 Admin Center? if you have access, we need the Extended message trace (EMT) from Exchange admin center.
• I need you to send me the Non delivery report (NDR) in the **** Private Messages - Microsoft Community. Check for specific error Email non-delivery report (NDR) and SMTP errors in Exchange Online - Exchange | Microsoft Learn.
• Do you have hybrid configuration or environment? or running as fully cloud environment?

Please understand that our initial response may not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution.

Thanks for choosing the MS community.

Looking forward to your response and have a great day ahead!!

Sincerely

S M Nazmun Nur | Microsoft Community Moderator