This document explains at a high level some parts of chasquid's message
processing, in particular how messages flow through the system.
- Client connects to chasquid on the smtp or submission ports, and issues
- Client optionally performs STARTTLS.
- Client optionally performs AUTH.
- Check that this is done over TLS.
- Client sends MAIL FROM.
- Check SPF.
- Check connection security level.
- Client sends one or more RCPT TO.
- If the destination is remote, then the user must have authenticated.
- If the destination is local, check that the user exists.
- Client sends DATA.
- Client sends actual data, and ends it with '.'
- Run the post-data hook. If the hook fails, return an error.
- Parse the data contents to perform loop detection.
- Add the required headers (Received, SPF results, post-data hook output).
- Put it in the queue and reply success.
Before accepting a message:
- Create a (pseudo) random internal ID for it.
- For each recipient, use the alias database to expand it, add the results to
the list of final recipients (which may not be email).
- Save the resulting envelope (with the final recipients) to disk.
Queue processing runs asynchronously, there's a goroutine for each message
which does, in a loop:
- For each recipient which we have not delivered yet:
- Attempt delivery.
- Write to disk the results.
- If there are mails still pending, wait for some time (incrementally).
- When all the recipients have completed delivery, or enough time has passed:
- If all were successful, remove from the queue.
- If some failed, send a delivery status notification back to the sender.