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The Event Hubs Standard tier does allow message retention periods longer than 24 hours, for a maximum of seven days. If the size of the total number of stored events exceeds the storage allowance for the number of selected throughput units (84 GB per throughput unit), the size that exceeds the allowance is charged at the published Azure Blob storage rate. The storage allowance in each throughput unit covers all storage costs for retention periods of 24 hours (the default) even if the throughput unit is used up to the maximum ingress allowance.
Hope this helps.
Sourced from FAQ - Azure Event Hubs