Inbound email that does not lose anything

Receiving email is the least glamorous part of Fridgedoor and the one with the worst failure mode. Nobody praises an inbox that works. Everyone remembers the customer who insisted they replied.

This release is a fortnight spent on that, and the changes are all of the same kind: a message that arrives must become an enquiry exactly once, and must not be able to disappear.

• Mail addressed to several of your addresses at once was being stored for only the last recipient. It is now stored for every one.
• A message delivered twice — which happens routinely, because a sending server that does not hear an acknowledgement will try again — was becoming two enquiries. It is recorded once.
• One undeliverable recipient could take the whole message down with it, so a single bad address meant nobody got it.
• A burst of mail could degrade rather than queue.
• A restart could drop a message that was mid-delivery, rather than letting the sender retry.

None of this is visible when it is working, which is the point. If you have ever had to ask a customer to send something again, this is the release that was meant to end that.