Chatmail: Delivery latency profiling

[s0ph0s-dog]

This is part of a series of issues tracking chatmail support in Mox.

To improve the user experience of Mox as a chatmail server, I'd like to spend some time profiling the message delivery/acceptance pipeline. I'd like to see if there are any opportunities for me to improve the latency between when submission completes and when an idle IMAP client is notified that a new message is available. I don't know for sure if this will be fruitful, but I'd like to learn more about Go profiling. So, even if it isn't, it will still be a useful learning experience :)

[mjl-]

Indeed, sounds useful! I would start not with profiling, but by enabling trace-level logging and looking at what mox is doing, comparing timestamps/durations between log lines.

My hunch is that most time is spent on handling incoming smtp deliveries, due to spf/dkim/dmarc/spam-filtering checks, which involves making DNS requests (having a local caching recursive DNS resolver should help).

Submitting to the queue is less involved and I wouldn't expect many delays there, starting delivery from the queue should also not have any delays. Likewise for sending out the notification for IMAP IDLE connections.

Of course, this is just a hunch, and delays may be in unexpected or innocuous looking places.