Where can I find the Office 365 sender support form?
Michael Ko
Co-founder & CEO, Suped
Published 25 May 2025
Updated 18 Aug 2025
6 min read
Dealing with email delivery issues can be incredibly frustrating, especially when your messages are bouncing back with errors like 451 4.7.500 Server busy. Please try again later. This often points to a temporary block by the recipient's mail server, and with Office 365 (now Microsoft 365) being a dominant player, encountering blocks there is a common concern for senders. My clients frequently ask about the specific support channels available for Office 365, particularly a sender support or delisting form.
Many senders confuse the support mechanisms for consumer Outlook.com accounts (formerly Hotmail) with those for enterprise Microsoft 365 environments. While Microsoft does offer various support avenues, pinpointing the correct form for Office 365 deliverability issues, like IP blocklisting (or blacklisting) or reputation problems, is key to getting a quick resolution. This guide will help you navigate directly to the appropriate resource.
Navigating Microsoft 365 sender support
When you face deliverability challenges with emails sent to Office 365 recipients, the primary tool you'll need is the Microsoft 365 Sender Delist Portal. This portal is specifically designed for senders whose IP addresses have been blocked (or blacklisted) by Exchange Online Protection (EOP), which is the built-in anti-spam and anti-malware service for Microsoft 365. It's important to differentiate this from the Outlook.com sender support, which is for consumer-facing email issues.
To access the correct form, you should navigate directly to the Microsoft 365 Sender Portal. You will need to be logged in with a valid Microsoft account to submit a request. This portal allows you to check the status of an IP address and submit a delisting request if it's currently on a Microsoft blocklist (or blacklist).
While there is a general Outlook.com sender support page for consumer domains, it is not the correct avenue for resolving deliverability issues impacting Microsoft 365 business email addresses. Using the wrong form can lead to delays and frustration, as your request may not reach the appropriate team. Always ensure you are using the specific portal for Office 365.
Important distinction
The Microsoft 365 Sender Delist Portal (sender.office.com) is for enterprise-level Office 365 (Microsoft 365) delisting requests related to IP blocks and reputation issues affecting business domains. Do not use the Outlook.com sender support forms for these issues, as they are intended for personal email accounts.
Essential information for your delisting request
Before submitting a delisting request, it is crucial to gather all necessary information. Microsoft will require specific details to process your request efficiently. The more comprehensive and accurate the information you provide, the better your chances of a swift resolution.
You will need the IP address (or addresses) that are experiencing delivery issues. You can usually find this in your bounce messages, mail server logs, or by using an online IP checker. Additionally, collecting specific bounce messages, especially the full error codes and descriptions from Microsoft, is highly beneficial.
Example bounce messagetext
550 5.7.1 Service unavailable, Client host [x.x.x.x] blocked using Spamhaus. To request removal from this list see http://www.spamhaus.org/lookup.html
Provide any context surrounding the issue, such as recent changes in your sending volume, new IP addresses, or campaigns that might have triggered the block. Understanding why your IP was blocklisted (or blacklisted) is the first step toward preventing future occurrences and demonstrating to Microsoft that you have addressed the root cause. This information will help them assess your request more accurately.
Information to gather
Blocked IP address: The specific sending IP(s) that are being blocked.
Full bounce messages: Copy-paste the exact error messages received.
Sending domain: The domain associated with the problematic emails.
Context to provide
Recent sending behavior: Any sudden spikes in volume or changes.
Steps taken: Describe what you have done to mitigate the issue.
Nature of emails: Transactional, marketing, etc.
Proactive strategies to maintain deliverability
While resolving current blocks is important, the best approach to email deliverability is prevention. Implementing strong authentication protocols and maintaining excellent sending hygiene will significantly reduce your chances of being blocklisted (or blacklisted) by Microsoft 365 or any other major inbox provider.
Always ensure your SPF, DKIM, and DMARC records are correctly configured. These authentication methods verify that your emails are legitimate and prevent spoofing. Microsoft places a high emphasis on authenticated email, especially with their new sender requirements. Maintaining a clean email list by regularly removing inactive or invalid addresses, and sending relevant content that recipients engage with, also plays a critical role in your sender reputation.
Monitor your email deliverability metrics and sender reputation actively. Keeping an eye on bounce rates, spam complaint rates, and open rates can alert you to potential issues before they escalate into a full block. If you see signs of trouble, act quickly to diagnose and remedy the underlying cause.
Best practice
Impact on deliverability
Implement SPF, DKIM, and DMARC
Verifies sender identity, reduces spam classification, improves trust with Microsoft 365.
List hygiene: Regularly clean your subscriber lists to remove invalid addresses and unengaged users.
Reputation monitoring: Keep an eye on your sending reputation and promptly address any negative trends.
After submission: expectations and next steps
After submitting your delisting request through the Microsoft 365 Sender Delist Portal, you will typically receive an automated confirmation. The response time for a resolution can vary. In many cases, if the issue is straightforward and you have addressed the underlying cause of the block, delisting can happen within a few hours to a few days.
It's common for Microsoft to provide automated responses initially. If your issue isn't resolved quickly, or if you continue to experience problems, it may be necessary to revisit your sending practices and ensure all authentication mechanisms are robust. You can also review guidance on troubleshooting email delivery issues in Microsoft 365 for more in-depth solutions.
Views from the trenches
Best practices
Always use the correct Microsoft 365 Sender Delist Portal for business email issues.
Verify your IP address and gather all bounce message details before submitting a request.
Implement and maintain SPF, DKIM, and DMARC for email authentication.
Gradually warm up new IP addresses and domains when sending high volumes of email.
Regularly monitor your sending reputation and email deliverability metrics.
Common pitfalls
Using the Outlook.com sender support form for Office 365 business email problems.
Not providing sufficient detail (IP, full bounce message, context) in the delisting request.
Failing to address the root cause of the block, leading to repeated listing.
Sending a high volume of emails from a new or cold IP without proper warm-up.
Ignoring DMARC reports or not acting on authentication failures.
Expert tips
For persistent issues, ensure your email infrastructure's SPF and DKIM are perfectly aligned.
If your IP is frequently blocked, consider your email content and audience engagement.
Automated responses are common; be patient but also thorough in your initial submission.
Review your sending logs for any signs of compromise or unauthorized sending.
Remember that delisting is often temporary if the underlying cause isn't fixed.
Marketer view
A marketer from Email Geeks says they found the sender.office.com link to be the correct one for Office 365 delisting, distinguishing it from Outlook.com support.
June 15, 2023 - Email Geeks
Expert view
An expert from Email Geeks clarified that OLC (Outlook Consumer) links are not for Office 365 issues, as these are related to Outlook.com or Hotmail.
June 15, 2023 - Email Geeks
Achieving consistent deliverability
Locating the correct Office 365 (Microsoft 365) sender support form is the first critical step in resolving deliverability issues, particularly IP blocklists (or blacklists). By going directly to the Microsoft 365 Sender Delist Portal and providing accurate, comprehensive information, you significantly improve your chances of a successful delisting.
Beyond reactive measures, prioritizing proactive email authentication, list hygiene, and reputation monitoring will help prevent future blocks and ensure your legitimate emails consistently reach the inbox. Continuous attention to these best practices is essential for long-term email deliverability success in any environment, including Microsoft 365.
