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When sending from our exchange mail server to the domain: outlook.sk, the response is returned - undeliverable: error: 550 5.7.1 .
Blocking due to IP address blacklisting. However, you are blocking the entire subnet of addresses: <Removed PII>. Our address is <Removed PII>. However, this address is clean. This can be verified here:
https://mxtoolbox.com/SuperTool.aspx?action=blacklist%<Removed PII>&run=toolpage#
Please unblock the address: <Removed PII>
Thank you
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Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.
Hi @Jechort Tomáš
Thanks for reaching out to the Microsoft Q&A forum. Based on your description, I understand you're unable to deliver emails to outlook.sk and are receiving a 550 5.7.1 NDR (Non-Delivery Report) error.
Based on my research, please ensure that your DNS configuration, especially your MX and SPF records, is correctly set up and verified to be working properly.
1.Please check the health status of your domain in the Microsoft 365 Admin Center to confirm whether it is marked as Healthy.
2.If your MX record status shows as "error", please follow the recommended troubleshooting steps to resolve.
For detailed guidance, you can refer to this official article: Fix NDR error 550 5.7.1 in Exchange Online - Exchange | Microsoft Learn
If you have already checked your DNS records and confirmed that their status is normal, the next step is to seek specialized support from the Microsoft Support Team. They have access to internal tools and databases, which allows them to investigate more deeply and assist you more effectively than a forum moderator with limited resources like myself.
To help speed up and smoothen the support process, please prepare the following information in advance:
Here are the official ways to contact the Microsoft Support Team:
Option 1: Contact via Phone
You can reach Microsoft Support through their customer service phone numbers: Customer service phone numbers - Microsoft Support.
Important Note: You may first interact with an AI assistant before being connected to a human agent. Please answer the questions carefully to ensure you're routed correctly. Having your information ready will help speed up the process.
Please be aware that this team is often handling a high volume of cases. It may take 3–10 business days for them to get back to you.
Option 2: Create a Ticket via Microsoft 365 Admin Center
You can submit a support ticket directly through the Microsoft 365 Admin Center.
For step-by-step guidance, please refer to: Get support - Microsoft 365 admin | Microsoft Learn
I sincerely hope this information partially clarifies your situation and assists you in planning your solution. Please do not hesitate to reply if you have any updates.
Thank you for your understanding.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.
Hello,
thanks for the quick response. We completely misunderstood each other. I have all the records correctly. I have the domain with me. I can't send e-mail to a domain hosted by Microsoft. Microsoft blocks a certain range of IP addresses for reception on its servers. I don't know why it blocks the entire range, including our address, when another address from the public address range is on the blacklist, thus preventing delivery to many other people, such as our company, which has everything in order. I need someone from Microsoft to unblock the range of addresses, because they are not on the blacklist and block only the address from the range that is listed on the blacklists.
I have listed the addresses above.
Thank you for your help
Hi @Jechort Tomáš
Thanks so much for the clarification
I mentioned DNS record configuration because it’s one of the recommended steps in the article that addresses error 550 5.7.1 NDR. It’s often a helpful place to start when narrowing down the cause.
If your DNS settings are already in good shape, the next step would be to reach out to Microsoft Support.
Unfortunately, as a forum moderator, I don’t have the ability to request IP unblocking or make changes to Microsoft’s filtering policies. The best way forward would be to contact Microsoft Support directly using the two methods I mentioned earlier. They’re the ones who can investigate the block and take appropriate action if your IP is being incorrectly filtered due to the wider range.
I truly appreciate your patience and the effort you’ve put into resolving this. Please feel free to reach out if there’s anything else I can help with.
Hi @Jechort Tomáš
I hope this message finds you well.
I wanted to follow up and check if you've made any progress with the Support Team since our last exchange.
In the meantime, I came across a helpful link that might assist with delisting your IP address: https://sender.office.com/. After submitting a delist request, please note that it may take up to 24 hours or more for Microsoft to verify and approve it.
If there are any new updates or if you need further assistance, please feel free to share. I’m here to help.
Hi @Jechort Tomáš
Hope you're having a good day.
I continued our conversation via a private message. If you have a moment, please check them out.
If you have an update or further questions, do not hesitate to contact me.
Thank you for your time.