Investigating - Email Delivery Issues for Email V1 Clients

Update timeline

1. investigating May 04, 2026, 11:19 PM UTC

   We are currently experiencing an intermittent deliverability issue with Email V1 Clients. During this time emails may not be received for some recipients. This will affect Registration, Marketing, Networking & Abstracts. We will provide updates regularly.

2. investigating May 05, 2026, 01:21 AM UTC

   We are continuing investigation of an intermittent Email Delivery Issues for Email V1 Clients.

3. monitoring May 05, 2026, 03:50 AM UTC

   The root cause of this issue has been identified: several of Stova’s IP addresses were added to the Spamhaus blocklist (DNSBLs) utilized by major ISPs. The affected IPs have since been removed from the Spamhaus blocklist. However, as mail systems do not query Spamhaus in real time, service improvements will become visible within 1–24 hours depending on cache clearance, with some instances potentially taking up to 48 hours. As a proactive measure, we have also submitted a request to Microsoft to remove the affected IPs from their blocking system. We will continue to monitor the situation closely and provide updates as needed.

4. investigating May 07, 2026, 01:44 PM UTC

   The email delivery issue affecting Email V1 clients has expanded. Our EU sending infrastructure is now also affected, in addition to the previously reported NA and APAC regions. Cause: One of our V1 sending IPs has been re-listed on the Spamhaus blocklist, and our EU sending IP has also been listed. We are working directly with Spamhaus to identify the underlying cause and to prevent further listings. Actions taken: Delisting requests have been raised with Spamhaus for all affected sending IPs and domains Direct delisting requests have been submitted to Microsoft to speed up clearance on their internal systems Our development team is reviewing sending patterns and authentication configurations across V1 client traffic to address contributing factors What to expect: Recipient mail systems do not query Spamhaus in real time. They cache results, typically for 1 to 24 hours, with some Microsoft systems taking up to 48 hours. Even after delisting, some emails may continue to bounce during this window until the caches refresh. We are monitoring V1 deliverability across all three regions and will update this page as the situation progresses.

5. investigating May 08, 2026, 09:37 AM UTC

   Identified - The email delivery issue affecting Email V1 clients across NA, APAC, and EU regions is ongoing. Our V1 sending IPs and associated domains remain listed on the Spamhaus blocklist, and Spamhaus has confirmed the listings are due to low reputation signals from associated domains. Cause: There is no direct contact channel with Spamhaus and no guaranteed response time on our delisting tickets. Recipient mail systems also cache blocklist results, typically for 1 to 24 hours, with some Microsoft systems taking up to 48 hours. Even after delisting completes, emails may continue to bounce during this cache window. Actions taken: Delisting requests have been raised with Spamhaus for all affected sending IPs and domains Direct delisting requests have been submitted to Microsoft to speed up clearance on their internal systems Our development team is reviewing sender authentication patterns (SPF, DKIM, DMARC) across V1 client traffic to address contributing factors and reduce the likelihood of re-listing Recovery path: Affected clients have been contacted directly with two migration options to restore reliable sending: migration to our more performant email server (Mailgun-backed) or connection to your own SMTP server. To opt in to either path, or to enquire further, please contact [email protected].

6. identified May 08, 2026, 09:39 AM UTC

   The issue has been identified and a fix is being implemented.

7. identified May 08, 2026, 09:47 AM UTC

   We are continuing to work on a fix for this issue.

8. investigating May 13, 2026, 07:48 AM UTC

   The status of the V1 email delivery issue remains under active investigation. Spamhaus and Microsoft delisting requests remain open across all affected V1 sending IPs and associated domains. Neither provider publishes processing timelines, and we are not in a position to forecast a confirmed delisting date. We will continue to push both tracks and update this page as the position changes. In parallel, our V2 email migration programme is running at pace. V2 is Mailgun-backed with dedicated DKIM and SPF authentication per client domain, and routes around the V1 IP reputation issue entirely. Clients already on V2 are unaffected by the current V1 listings. What clients on V1 should expect: Email delivery from V1 may remain intermittent until Spamhaus delisting completes and recipient mail system caches refresh (typically 1 to 24 hours after delisting, with some Microsoft systems taking up to 48 hours). Bounces and low open rates during this window should be assumed to be incident-related. Recovery path: Clients wishing to opt in to the V2 or V3 (SMTP) migration, or who need delivery logs for affected sends, should contact [email protected] and reference this incident. We are fast-tracking migration requests. We will continue to monitor V1 deliverability across NA, APAC, and EU regions, and update this page as the situation progresses.

9. investigating May 21, 2026, 02:37 PM UTC

   The V1 email delivery issue remains under active investigation. Delisting requests for our NA and EU sending IPs remain open with Spamhaus and Microsoft, and both tracks are being actively pushed. Neither provider publishes processing timelines, so we are not able to confirm a delisting date. Our AU region has progressed and is under verification. Clients who need reliable sending sooner can opt in to our V2 or V3 (SMTP) migration by contacting [email protected] and referencing this incident. We are fast-tracking migration requests. We will continue to monitor and update this page as the position is confirmed.

10. investigating May 21, 2026, 02:38 PM UTC

    We are continuing to investigate this issue.

11. resolved May 28, 2026, 09:50 AM UTC

    Resolved - Email Delivery Issues for Email V1 Clients We have moved to a durable resolution for this issue. Rather than rely on temporary measures, we are migrating affected accounts to a more performant email server (V2 or V3 SMTP) that provides stronger, more reliable deliverability and routes around the V1 reputation issue entirely. Our support team is reaching out directly to affected clients to begin this migration, which can typically be completed within 24 to 48 hours once DNS updates are in place. Clients who want to start sooner can contact [email protected] and reference this incident, and we will prioritise the setup. We are marking this incident resolved here, as all further action is moving to direct migration with affected clients. For any questions, please contact [email protected]