Oh wow, a 23-page write up about how the author misunderstood AWS Lambda's execution model [1].
> It emits an event, then immediately returns a response — meaning it always reports success (201), regardless of whether the downstream email handler succeeds or fails.
It should be understood that after Lambda returns a response the MicroVM is suspending, interrupting your background HTTP request. There is zero guarantee that the request would succeed.
1: https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtime-...
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