From SNS FAQ, i know there is a retry policy for SNS to SQS, but do they guarantee at least one message delivery to SQS?
Please give official quotes.
See https://aws.amazon.com/sqs/faqs:
Q: Does Amazon SNS provide at-least-once delivery of messages to Amazon SQS queues?
Amazon SNS is designed such that each message is delivered at least once to Amazon SQS standard queues.