Export a broadcast's recipients as CSV

Downloads a broadcast's recipients as a CSV file, one row per recipient. The header names ten columns, in this order: recipient, status, rejection_reason, open_count, click_count, processed_at, delivered_at, processing_latency_ms, delivery_latency_ms and total_latency_ms.

rejection_reason is filled only on a status: rejected row and names why the message was never sent, which is not why it bounced. A bounce happens after the send, so no column here carries bounce_type or bounce_code: read List recipients of a broadcast for those. The three latency columns are milliseconds, and each is empty until the milestone it measures has happened: processing_latency_ms from the send being accepted to the message being prepared for delivery, delivery_latency_ms from prepared to the receiving mail server accepting it, and total_latency_ms the accepted-to-delivered time end to end.

A text cell whose first character is =, +, -, @, a tab or a carriage return is written with a leading apostrophe, so a spreadsheet reads it as text rather than as a formula. Nothing else is prefixed, so a value that begins with an apostrophe of its own is written unchanged: strip a leading apostrophe only when one of those six characters follows it, before matching recipient back to the API.

The file is complete or it is refused: a broadcast with more recipients than one file carries returns a 422 naming the limit rather than a truncated download. Pass to to export one address, or page List recipients of a broadcast, which has no limit.