Evri: 4.5 million messages a day, every day

"Your parcel is 5 stops away." The service behind that message sends 4.5 million of them a day, and we made it dependable.

The problem

Evri (then Hermes) had a notification service built by a third party and handed over mid-flight. During the handover it suffered a serious production incident. 245 million parcels a year don't pause while you find your feet.

What we did

Diagnosed and fixed the incident, then went hunting: a series of latent defects found and resolved before they became the next one. Reliability went up immediately and stayed up.

What it runs on

Serverless event-driven AWS: Lambda off SQS, DynamoDB holding overnight and reminder messages, everything flowing to Parquet and Athena for the dashboards half the business reads. Back-office staff design email, push and SMS templates themselves, tested through Email on Acid with snapshot comparisons before anything ships.