Incident Window
Start: 2026-09-23 12:30 UTC
End: 2026-09-23 18:45 UTC
Impacted Services
Outbound multimedia messaging (MMS) sent to subscribers on AT&T's network via 10-digit long code (10DLC) experienced significant delivery delays.
Summary
On September 23rd, Bandwidth's automated monitoring systems detected that outbound multimedia messages to subscribers on AT&T's network were not being delivered within expected timeframes, triggering an alert and initiating Bandwidth's incident response process.
Bandwidth confirmed that a portion of outbound multimedia messages was experiencing delivery delays of up to an hour or more. The issue was isolated to multimedia messages destined for AT&T's subscribers only. No other carriers or message types were affected.
Investigation determined that the root cause was a configuration change on AT&T's network that caused a mismatch between AT&T's messaging platform and the number of processing channels it was expecting, resulting in messages queuing rather than being delivered promptly.
To resolve the incident, AT&T corrected the configuration mismatch and restored the affected processing channels. Following the fix, delivery times returned to normal levels, with maximum observed delays dropping to under 30 seconds shortly after resolution. Bandwidth confirmed full service restoration on September 23rd at 18:45 UTC.
Root Cause
Multimedia message delivery delays were caused by a change made on AT&T's messaging platform that was not fully applied across all required components, leaving a mismatch between the number of processing channels configured and the number the platform expected to have available. This mismatch caused messages to queue rather than deliver promptly, extending delivery times well beyond acceptable thresholds for a meaningful portion of affected traffic.
Preventive Actions
AT&T has updated its internal documentation to ensure all services requiring updates are identified prior to any future change being implemented.