[POSTMARK] ISP errors sending to Gmail addresses - all pods

Update timeline

1. investigating Nov 13, 2025, 08:56 PM UTC

   Kustomer is aware of an event affecting kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is currently working to identify the cause of this issue in an effort to implement a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support [email protected] for any further questions or updates.

2. investigating Nov 13, 2025, 09:31 PM UTC

   Kustomer is aware of an event affecting kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is continuing to work toward identifying the cause of this issue in an effort to implement a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support [email protected] for any further questions or updates.

3. investigating Nov 13, 2025, 10:10 PM UTC

   Kustomer is aware of an issue impacting emails sent from @kustomerapp.com addresses, which may result in delivery failures to Gmail recipients. Our team is actively investigating the cause and working to implement a resolution. We will provide another update within 30 minutes. For further questions or updates, please contact Kustomer Support via Chat or Email.

4. investigating Nov 13, 2025, 10:43 PM UTC

   Kustomer continues to investigate an issue affecting emails sent from @kustomerapp.com addresses, which may cause delivery failures to Gmail (@gmail.com) recipients. Our team is working diligently to identify the root cause and implement a fix. We will share another update within 30 minutes. For any questions or further assistance, please contact Kustomer Support via Chat or Email.

5. investigating Nov 13, 2025, 11:27 PM UTC

   Kustomer is still investigating an ongoing issue impacting emails sent from @kustomerapp.com addresses, which may result in delivery issues when reaching Gmail (@gmail.com) recipients. Our team continues to work toward identifying the root cause and implementing a resolution. We will provide another update within 30 minutes. For any questions or additional support, please reach out to Kustomer Support via Chat or Email.

6. identified Nov 13, 2025, 11:45 PM UTC

   Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is still continuing to work on implementing a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

7. identified Nov 14, 2025, 12:17 AM UTC

   Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is still continuing to work on implementing a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

8. identified Nov 14, 2025, 12:49 AM UTC

   Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is still continuing to work on implementing a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

9. identified Nov 14, 2025, 01:20 AM UTC

   Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is still continuing to work on implementing a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

10. identified Nov 14, 2025, 01:59 AM UTC

    Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. Our team is still continuing to work on implementing a resolution. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

11. identified Nov 14, 2025, 02:34 AM UTC

    Kustomer has identified an event affecting mail.kustomerapp.com email addresses that may cause messages sent to gmail.com addresses to bounce. A fix is being rolled out incrementally to customers and we continue to monitor the situation as it improves. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

12. identified Nov 14, 2025, 03:04 AM UTC

    A fix is being rolled out incrementally to customers and we continue to monitor the situation as it improves. Please expect additional updates within the next 30 minutes, please reach out to Kustomer Support via Chat or Email for any further questions or updates.

13. monitoring Nov 14, 2025, 03:17 AM UTC

    Kustomer has implemented a fix, which we are currently monitoring, to address the event affecting [POSTMARK] ISP errors. Our team is currently monitoring this update to ensure the issue is fully resolved. Please expect further updates within the next 30 minutes, and reach out to Kustomer support via Chat or Email if you have additional questions or concerns.

14. resolved Nov 14, 2025, 04:01 AM UTC

    Issues encountered during sending emails to gmail addresses have been resolved. Within the hour, the issue should be fully resolved as changes propagate throughout DNS records. If you experience any further problems, please reach out to support and we'll look into it with high priority.

15. postmortem Dec 04, 2025, 02:25 PM UTC

    # **Summary** New, tightened bulk sender rules by Gmail went into effect in November 2025, which affected Kustomer’s ability to deliver transactional emails to Gmail mailboxes. Specifically, DMARC alignment failures due to messages not being aligned to the from domain resulted in emails sent from [mail.kustomerapp.com](http://mail.kustomerapp.com) domain to [gmail.com](http://gmail.com) addresses to be blocked. ‌ **Root Cause** Beginning in early November 2025, Gmail rolled out stricter requirements for organizations that send large volumes of email. Because Kustomer sends more than 5,000 messages per day to Gmail addresses, Gmail classifies our traffic as “bulk sender” traffic and applies stronger authentication checks. Many of the emails sent from Kustomer customers through Postmark were not fully meeting Gmail’s updated authentication requirements. Although the messages were being sent from addresses that looked like they belonged to each customer \(eg: [[email protected]_](mailto:[email protected])\), the DMARC policy check was now failing. As a result, Gmail could not verify that these messages truly came from the domain shown in the “From” address. When Gmail applied its new enforcement rules, any email that did not clearly authenticate as coming from the correct domain was blocked before delivery. This caused a spike in rejected emails for customers sending to Gmail inboxes. ‌ # **Timeline** **Early November 2025** Gmail begins enforcing newly updated bulk-sender requirements for high-volume senders. These rules require stricter domain authentication for all messages sent to Gmail inboxes. **Nov 11, 2025** ‌ **2:18 PM EST — Initial Reports**Customer support teams begin receiving reports that emails sent to Gmail addresses are bouncing or failing to deliver. **2:46 PM EST — Issue Confirmed** Responding teams identify that the issue is widespread and related to Gmail’s new enforcement behavior. **3:11 PM EST — Root Cause Narrowed Down**Misalignment in required email authentication settings is identified as the likely cause of Gmail rejecting messages. **4:00 PM EST - 7:45 PM EST – Fix Validation** Responding engineers work on implementing and validating the fix. **8:01 PM EST — Fix deployment**The necessary configuration updates are confirmed, including correcting DNS records so Gmail can properly verify the sender. **10:00 PM–11:00 PM EST — Remediation & Stabilization**Updated DNS records are applied across affected customer domains. Gmail begins accepting previously rejected messages, and email delivery to Gmail addresses returns to normal. ‌ **Lessons/Improvements** **Improved Email Authentication Setup Across All Customers:** All customer organizations now have the correct DNS records and Postmark sender signatures in place to ensure their messages meet Gmail’s authentication requirements. **Enhanced Monitoring for Email Delivery Issues:** We are implementing new logging and alerting to detect spikes in email bounces earlier, allowing us to respond more quickly if delivery issues arise in the future. **Stronger Setup Process for New Integrations:** Going forward, all new Postmark email integrations will be configured with the correct authentication settings from the start to prevent this issue from occurring.