Zanda - SMS Delivery – Incident details

Post-Mortem: SMS Delivery Incident - 25 June 2026

Following the resolution of this incident, we want to provide a fuller post-mortem for transparency.

What happened

As our SMS provider has continued their investigation, it has been determined that a component within their messaging platform responsible for routing outbound messages stopped working. This was a widespread event.

As a result, messages were not processed as expected, and a backlog built up. They then stopped accepting new messages from platforms like Zanda. The SMS provider was not able to directly fix the impacted components, so they provisioned new infrastructure. Outbound messages were then routed via this infrastructure. They then started accepting messages again, and message sending resumed as normal.

What we did

We received some initial reports from customers stating that SMS messages had not been received by clients. We commenced an investigation immediately, which identified that SMS messages from Zanda were being sent to our SMS provider correctly, but that they were experiencing a processing issue, as described above.

On our end, we were able to identify new messages that were not being accepted by the SMS provider. We then flagged these, requeued them, and sent them once the SMS provider had provisioned the new infrastructure.

We were also in contact with the SMS provider during this time and received updates as they worked through the issue. We also posted a notice in Helperbee and commenced this incident page so all Zanda customers could be kept up to date as the situation unfolded.

Impact

The vast majority of SMS messages sent on 25 June were delivered correctly and on time. During the affected period, SMS messages were sent, but after a delay of anywhere from a few minutes to several hours.

Our initial understanding was that all SMS messages received by our SMS provider were sent. However, they are still reconciling their SMS logs. We have been advised that some SMS messages may have been delivered multiple times, and that some messages (sent during the earlier phases of the incident) may not have been sent at all.

We sincerely apologise for the disruption this may have caused.

What we’re doing

As our SMS provider continues its reconciliation of SMS messages, we will be applying credits for any SMS messages that were not delivered, as well as ensuring that there were no charges incurred where SMS messages were sent multiple times.

While we have confidence that our SMS provider understands the significance of an incident like this, we are also ensuring that they are fully aware of the impact this had on Zanda’s customers and their clients.

We take the reliability of our platform seriously and will continue to monitor our SMS delivery closely going forward.

Thank you for your patience and understanding throughout this incident.

This incident has been resolved. A fix has been implemented by our SMS provider, and validation testing has been completed to confirm that message sending and delivery are functioning as expected.

We are not currently observing any further issues related to this incident. Our team will continue to closely monitor messaging performance to ensure stability.

We understand how important reliable SMS delivery is to your practice and sincerely apologise for the disruption this may have caused. Thank you for your patience while this was investigated and resolved.

The SMS delivery issue has been resolved. All failed messages have been requeued and successfully delivered across UK, AU, and US regions.

Our SMS provider has implemented a fix and is actively monitoring their services. We are also continuing to monitor to ensure the issue does not reappear.

We are continuing to monitor this incident closely with our SMS provider.

Their engineering teams, together with external resources, are treating this as a high-priority issue and are actively working to restore normal SMS delivery as quickly as possible.

At this stage, there is still no estimated time for resolution. We will continue to provide updates here as soon as further information becomes available.

Thank you for your continued patience and understanding.

We are continuing to monitor this issue closely with our SMS provider, who are actively investigating the root cause of the incident affecting SMS delivery.

At this stage, they have not yet been able to identify the underlying cause and are unable to provide an estimated time for resolution. To minimise further disruption, they have implemented temporary measures to prevent additional message backlogs and duplicate SMS deliveries while their investigation continues.

As a result, some SMS messages may be delayed, fail to send, or require resending once the incident has been resolved.

We understand how important reliable SMS delivery is to your practice and sincerely apologise for the inconvenience. We will continue to provide updates here as soon as we receive further information from our SMS provider.