How to Fix sender.office.com Delist Portal Not Working
Question details
The user needs to remove a mail server IP from the Microsoft 365 blocklist, but the sender.office.com delist portal is experiencing service issues.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Trying to delist a newly assigned mail server IP to restore outbound email delivery to Microsoft 365 recipients.
- Observed behavior
- The sender.office.com portal repeatedly reports a temporary service issue, preventing the IP from being removed from the blocklist.
Ensure you have administrative access to your mail server and DNS records to verify your current email authentication setups.
Verify Email Security Configurations and Disable Open Relay
Before contacting support, ensure your server is correctly configured so it will not be re-blocked once delisted.
Microsoft requires strict adherence to email security protocols. If your server allows anonymous relay or lacks proper authentication, any delisting will be temporary.
Check your domain's DNS settings to ensure SPF, DKIM, and DMARC records are correctly published and valid.
Use a Telnet client to connect to your mail server on ports 25, 465, and 587. Attempt to send an email without authenticating to confirm anonymous relay is disabled.
Ensure you have a valid, monitored postmaster address configured on your domain, as blocklist administrators may use this for verification.
Escalate the Issue via Microsoft Support
If the automated portal is unavailable, you must request manual intervention from Microsoft.
Use a Paid Outbound Relay Service Temporarily
Maintain business continuity and outbound email flow while waiting for Microsoft to resolve the delisting issue.
Enhance Your Productivity with WPS Office
While waiting for Microsoft 365 support to resolve your email server issues, consider trying WPS Office for your local document tasks. It is a highly compatible, lightweight, and free alternative to Microsoft Office that gets you working immediately.
- 1. Download WPS Office: Visit the official WPS website and download the installer for your operating system.
- 2. Install the Suite: Run the installer and follow the on-screen prompts to set up WPS Office on your device.
- 3. Open Your Documents: Launch WPS Office and instantly open, edit, and save your existing Microsoft Word, Excel, and PowerPoint files.
Frequently Asked Questions
Why is my newly assigned IP address already on the Microsoft 365 blocklist?
Newly assigned IPs often lack a positive sender reputation or may have been abused by a previous owner, causing Microsoft's automated spam filters to block them by default.
How do I know for sure that my IP is blocked by Microsoft 365?
You will receive a Non-Delivery Report (NDR) when emailing a Microsoft 365 user. The bounce message usually contains a specific error code (such as 5.7.606) indicating that your IP is banned.
Can I bypass the Microsoft blocklist if the delist portal is down?
Yes, by configuring your mail server to route outgoing messages through a reputable third-party outbound SMTP relay service, your emails will be sent from their clean IPs instead of your blocked one.
