blocked sender IP

Nivedita 40 Reputation points
2026-08-16T23:37:15.58+00:00

my email sender IP has been blocked by microsoft. I have written to delist@microsoft.com but have not received any response from them. It has been 2 days now. My business is impacted.. What is the next step for me?

Outlook | Web | Outlook.com | Email
Answer accepted by question author
SD - IA 179K Reputation points Independent Advisor
2026-08-18T03:12:57.3533333+00:00

Awesome! Thanks, Nivedita for letting me know. I would appreciate if the question is marked as answered to close it.

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  1. SD - IA 179K Reputation points Independent Advisor
    2026-08-17T16:40:05.4733333+00:00

    Thanks, Nivedita. Please fill the form I mentioned and let me know.

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  2. SD - IA 179K Reputation points Independent Advisor
    2026-08-17T03:53:59.91+00:00

    Hi,
    Typically, the Outlook teams do not work on weekends; hence the delay. I assume you also filled http://olcsupport.office.com/ page, since it is necessary as well. It should get solved in a day or two.

    I look forward to hearing from you to get the results of the troubleshooting.

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  3. AI answer

    2026-08-16T23:37:31.0633333+00:00

    If the NDR was 550 5.7.511 Access denied, banned sender, the next step is to send the message to delist@microsoft.com with the full NDR code and the blocked IP address. Microsoft states that contact is made within 48 hours with the next steps.

    If the NDR was instead a blocked IP error such as 550 5.7.606-649 Access denied, banned sending IP, use the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com/:

    1. Open the portal.
    2. Enter the email address that received the NDR.
    3. Enter the IP address shown in the error.
    4. Select Submit.
    5. Open the confirmation message sent to that address and select the confirmation link.
    6. Return to the portal and select Delist IP.

    After delisting, restrictions can take up to 24 hours or longer to clear.

    If mail is still blocked after following the NDR instructions, ask the Microsoft 365 recipient to open a Microsoft Support ticket on behalf of the sender. External senders typically can’t open Microsoft 365 support tickets directly.

    Also verify the sending server is not presenting a nonroutable private IP during SMTP and that reverse DNS is valid. Microsoft might reject senders that fail reverse-DNS lookup or advertise private ranges such as:

    • 192.168.0.0/16
    • 10.0.0.0/8
    • 172.16.0.0 - 172.31.255.255
    AI-generated content may be incorrect. Read our transparency notes for more information.

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