Email Service Disruption Due to Server Compromise - Email are not able to sent to gmail domain

Question

Dear Team,

Please be informed that our email server was compromised, which caused an email service disruption from 01-02-2026 (6:49 PM) to 02-02-2026 (3:50 PM).

Following this incident, for the past 7 days, we have been unable to send or receive emails specifically to/from [gmail.com] domains. However, email communication with other domains is working properly.

During the security breach, bulk emails were sent without authorization from the following accounts:

[Moderator note: personal info removed]

[Moderator note: personal info removed]

[Moderator note: personal info removed]

These emails were randomly triggered to multiple recipients without any sending limit, and we also received a high volume of spam and mail delivery failure notifications. Due to this activity, our server IP appears to have been blocked from your end for Gmail domain communication.

Answer 1

Please note that Q&A forum is a public platform, and moderators will modify the question to hide personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hello Arvind

Thank you for reaching out to the Microsoft Q&A. I'm sorry to hear about the server compromise and the ongoing email issues. Based on what you've described, it appears your email server's IP address has likely been flagged or blacklisted by Google's spam filters due to the unauthorized bulk sending. Gmail doesn't directly "block" IPs but uses sophisticated spam detection that can route emails to spam folders or reject them based on reputation. Since other domains work fine, this is likely specific to Google's filters.

First could you try to check blacklists. Verify if your server's IP is listed on public blacklists, which Gmail references. Use free tools like:

• MX Toolbox (mxtoolbox.com): Enter your IP and check for blacklisting.
• Spamhaus (spamhaus.org): Look up your IP.
• If listed, follow their delisting procedures

Next, submit a delivery issue report to Google, you can try Troubleshooting for senders with email delivery issues.

Note: This information is provided as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.

Hope this help.

---

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 2

It seems that your email server was compromised, which has led to a disruption in sending and receiving emails specifically to and from Gmail domains. This can happen when unauthorized bulk emails are sent from your server, causing your server's IP to be flagged or blocked by Gmail due to spam detection.

To address this issue, consider the following steps:

1. Secure Your Email Server: Ensure that your email server is secure and that any vulnerabilities are addressed to prevent future breaches.
2. Contact Gmail Support: Reach out to Gmail support to explain the situation and request the removal of any blocks on your IP address. Provide details about the incident and the corrective actions you have taken.
3. Authenticate Your Email: Make sure your email domain is properly authenticated using SPF, DKIM, and DMARC. This can help improve your email reputation and reduce the chances of being flagged as spam.
4. Monitor Sending Practices: Implement monitoring to ensure that your email sending practices comply with best practices, including limits on bulk sending and ensuring that recipients have opted in to receive communications from your domain.
5. Use Google Postmaster Tools: Utilize Google Postmaster Tools to monitor your domain's reputation and identify any issues affecting email deliverability.

By following these steps, you should be able to resolve the email service disruption and improve your email deliverability to Gmail domains.