> Also, hopefully the API you use to send email has a way to avoid duplicate emails, perhaps by attaching a unique ID to the request that's used to detect duplicate sends.

I think this is the interesting part. Storing a value in the table to be processed by a queue seems normal / not rocket science. But what happens when we 1. Call the API 2. The API succeeds 3. We crash before we can write success

Now we'll send duplicate emails. I don't think all APIs have ways to avoid duplicate emails/transactions, so that could be a hairy problem.