I agree - having to tell a database that something was processed, and fire off a message into RabbitMQ, say, is never 100% transactional. This would be my top reason to use this approach.
> With a Postgres queue, if you insert the job to send the email and then in a later part of the transaction, something fails and the transaction rollbacks, the email is never queued to be sent.
This is true - definitely worth isolating what should be totally separate database code into different transactions. On the other hand, if your user is not created in the DB, you might not want your signup email. Just depends on the situation.
> With a Postgres queue, if you insert the job to send the email and then in a later part of the transaction, something fails and the transaction rollbacks, the email is never queued to be sent.
This is true - definitely worth isolating what should be totally separate database code into different transactions. On the other hand, if your user is not created in the DB, you might not want your signup email. Just depends on the situation.