Suspicious Login Issues

How to Report and Block Spam Sent from Microsoft-Hosted Domains

Algirdas Jasaitis Oct 12, 2026 869 views

Question details

The user needs to stop receiving large volumes of spam from random domains hosted on Microsoft 365 or Azure without blocking legitimate emails that share the same IP addresses.

How to Report Spam Sent from Microsoft-Hosted Domains

Product: Microsoft 365
Device & OS: not provided
Scenario: Receiving frequent spam or phishing emails that appear to originate from Microsoft's hosted infrastructure.
Observed behavior: Spam messages are sent using Microsoft's shared IP addresses, making it difficult to block the spam without accidentally blocking legitimate domains hosted on the same infrastructure.

Before you start

Do not add Microsoft's shared IP addresses or domains directly to your blocklist, as this can severely disrupt legitimate incoming mail from other organizations.

Solution 1Recommended

Inspect Email Headers and Report Abuse

Examine the full message headers to identify the true sender or abused tenant, block them specifically, and report the abuse to Microsoft.

Because Microsoft 365 and Azure use shared infrastructure, blocking the visible IP address will block innocent users. By analyzing the email headers, you can pinpoint the specific sender address, domain, or abused tenant responsible for the spam.

Open full message headers

In your email client, open the spam message and locate the option to view message details, raw source, or full headers (often found under 'Properties' or 'View page source').

Identify the actual sender

Look for the 'Return-Path', 'X-Sender', or 'Authentication-Results' fields in the header to find the true originating email address or specific domain rather than the shared Microsoft IP.

Block the specific source

Add the exact sender email address or their individual domain to your email client's block list or spam filter rules.

Report to Microsoft

Forward the complete spam email, including its full headers, to Microsoft's official abuse-reporting channel (such as abuse@microsoft.com) to notify them of the compromised or abusive tenant.

Spoofed Addresses: Be aware that the visible 'From' address might be spoofed. Relying on the header authentication information is crucial to finding the actual source.

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Frequently Asked Questions

Why shouldn't I block Microsoft's IP addresses to stop spam?

Microsoft uses shared IP addresses for millions of legitimate business and personal accounts. Blocking these IPs at the firewall or email server level will likely prevent legitimate emails from reaching your inbox.

How can I tell if an email is actually from Microsoft or spoofed?

You must inspect the email headers and check the SPF, DKIM, and DMARC authentication results. If these checks fail, the email is likely spoofed and not genuinely sent from the domain it claims to represent.

What is the correct way to report abuse to Microsoft?

You should forward the suspicious email, ensuring the full message headers are included, to Microsoft's designated abuse-reporting email addresses (like abuse@microsoft.com) or submit it through their official security portal.

Microsoft Office Security Issues