POSTMASTER BLOCK

Secure the compromised Outlook.com account first, then use the diagnostic text in each Postmaster message to determine whether Outlook.com temporarily restricted the account or the recipient company rejected the email.

1. Complete the compromised-account cleanup

Because unauthorized access is confirmed, perform these steps in order:

1. On the affected computer, update the antivirus protection and run Virus & threat protection → Scan options → Full scan → Scan now.
2. After the scan finishes, change the Microsoft account password to a new, unique password.
3. Review Outlook.com’s connected accounts, forwarding, and automatic replies, removing anything you did not configure. Microsoft specifically includes these checks in its compromised-account recovery procedure.^1^
4. In Outlook.com, open Settings → Mail → Rules and delete unfamiliar rules. Also inspect Mail → Forwarding.
5. Review the account’s Recent activity. It displays sign-ins from the previous 30 days, including device or application information. Mark unfamiliar entries as This wasn’t me, then update the account’s security information and remove unrecognized trusted devices.^2^
6. Enable two-step verification or Microsoft Authenticator after confirming that all recovery email addresses and phone numbers belong to you.

Do not delete the Outlook.com address or alias merely because it was compromised. Deleting a Microsoft-domain alias can be permanent.

2. Identify what the Postmaster message actually says

Open one failed-delivery message and scroll to Diagnostic information for administrators. A legitimate Postmaster response normally means that one or more recipients could not receive the message; the detailed error identifies where it failed.^3^

Use the matching branch:

• Account temporarily blocked / unusual activity: Complete the identity-verification or security-code process on the Outlook.com unblock page. Outlook.com can temporarily block an account after detecting unusual sign-in activity.^4^
• Sending limit, quota, or too many recipients: Stop sending messages in batches. Contact one company at a time and allow the restriction to clear. Outlook.com limits daily recipients, recipients per message, and messages to people with whom the account has no established relationship; limits can also vary with usage history.^5^
• Spam or policy rejection by the recipient: That company’s mail system is rejecting the message. Send a short plain-text message with no attachment, link, signature, or multiple recipients. Add the address to Outlook.com Contacts and ask the company—through another channel—to add your address to its safe-senders list.^6^
• Invalid recipient, mailbox full, or recipient-server failure: Correct the address or contact the company through its website, telephone number, or support form. These are recipient-side delivery failures rather than a general Outlook.com block.^7^
• Storage full: Free space in both the Outlook.com mailbox and Microsoft cloud storage; Outlook.com cannot send or receive while that storage is full.^7^

Retype each recipient’s complete address instead of selecting an old Auto-Complete entry. Do not repeatedly resend the same rejected message, because repeated attempts can worsen rate or reputation restrictions.

3. Contact the companies without relying solely on email

For accounts fraudulently created in your name, use each company’s official account security, fraud, or privacy contact form or published telephone number. State that:

• Your email address was used without authorization.
• You dispute ownership of the account.
• You want the account frozen or closed.
• You want the email address removed.
• You can provide the relevant account-opening notification, but not passwords or one-time verification codes.

Keep the original registration notices and Postmaster reports as evidence. Do not click account-management links in unexpected messages; navigate to each company’s official website independently.

If the diagnostic says the Outlook.com account remains blocked after completing the security-code process, select Help in Outlook.com, enter the error, then choose Still need help? → Yes to request Outlook.com support.^4^

References

1. How to recover a hacked or compromised Microsoft account
2. What is the Recent activity page? | Microsoft Support
3. Failed delivery messages from the postmaster at outlook.com, microsoft.com, or service.microsoft.com | Microsoft Support
4. Unblock my Outlook.com account
5. Sending limits in Outlook.com | Microsoft Support
6. Sender Support in Outlook.com | Microsoft Support
7. Can't send or receive email in Outlook.com | Microsoft Support