A developer is investigating an issue in part of a company's application. In the application, messages are sent to an Amazon Simple Queue Service (Amazon SQS) queue. The AWS Lambda function polls mess

Question

Options

• AStandard SQS queues support at-least-once message delivery.
• BStandard SQS queues support exactly-once processing, so the duplicate email messages are
• CAmazon SES has the DomainKeys Identified Mail (DKIM) authentication incorrectly configured.
• DThe SQS queue's visibility timeout is lower than or the same as the Lambda function's timeout.
• EThe Amazon SES bounce rate metric is too high.

• A
  69% (20)
• B
  17% (5)
• C
  10% (3)
• E
  3% (1)

Explanation

Why A and D are correct:

Standard SQS queues guarantee at-least-once delivery (A), meaning a message can be delivered more than once - this is a fundamental SQS characteristic that directly causes duplicates. Additionally, if the visibility timeout is too short (D), a message becomes visible again in the queue before Lambda finishes processing it, causing a second Lambda invocation to pick up and process the same message - resulting in a second email.

Why the distractors are wrong:

• B is factually incorrect - Standard SQS does not support exactly-once processing; that's only available with SQS FIFO queues using deduplication IDs.
• C - DKIM is an email authentication/anti-spoofing mechanism; misconfiguring it affects deliverability and spam classification, not duplicate sends.
• E - A high bounce rate degrades your SES sending reputation and can lead to sending restrictions, but it has no mechanism that causes duplicate messages.

Memory tip: Think of the two causes as a queue problem and a timing problem. Standard SQS = "at least once" by design. Visibility timeout < Lambda timeout = the queue thinks processing failed and redelivers. If you're seeing duplicates with SQS + Lambda, always check these two first - they're the classic combination that causes this pattern.

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