Concider upgraing to RabbitMQ 4.3.x BTW https://endoflife.date/rabbitmq --
Best regards, Benoit TELLIER General manager of Linagora VIETNAM. Product owner for Twake-Mail product. Chairman of the Apache James project. Mail: [email protected] Tel: (0033) 6 77 26 04 58 (WhatsApp, Signal) On Aug 18, 2026 10:56 AM, from James A Via Server-user <[email protected]>Hi James Support Team, We are running a distributed Apache James deployment (v3.9.0) backed by Cassandra 4.1.x, RabbitMQ 3.x, and AWS S3 as our BlobStore. We are currently load testing. During our load testing, we observed a distinct issue with S3 throttling: With deduplication.enable=true: We experience recurring 503 SlowDown error spikes from AWS S3 under high write/spooling throughput. With deduplication.enable=false: The 503 SlowDown errors disappear entirely under the exact same traffic load. Because deduplication provides S3 cost and capacity savings, we want to keep it enabled. We suspect this may be caused by single-partition prefix hot-spotting in S3 when generating content-addressed SHA-256 BlobIds, or synchronous hash calculation bottlenecks under heavy concurrency. Could you please advise on: 1. Recommended s3.properties / blob.properties tuning for content-addressed deduplicated BlobStores at scale (e.g., prefix hashing / sub-bucket routing configurations to distribute S3 partition keys). 2. Recommended AWS SDK / connection pool settings (such as objectstorage.s3.http.concurrency or retry/backoff policies) inside James to gracefully handle S3 rate limits. 3. Any known fixes or improvements in more recent James releases regarding BlobStore deduplication and S3 partitioning. Thanks in advance for your guidance!
