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T

Wez Furlong 7aa80bc34a rollup.lua: add ip-based rollup

How it works:

* When the lowest preference MX host names match a pattern like
  `.mail.protection.outlook.com`, the message has its routing_domain
  set to a placeholder domain whose name ends with `.ip_rollup`.
* That results in a scheduled queue name like
  `foo.com!outlook.ip_rollup`, which makes it possible to know both the
  original domain and the fact that rollup is in use.
* `get_queue_config` can check to see if the routing_domain is set to
  something that ends with `.ip_rollup` to override the `mx_list`
  in the queue configuration with just the lowest preference IP
  addresses from the original domain.
* Now, instead of computing a site_name base around
  `foo-com.mail.protection.outlook.com`, which includes the individual
  original recipient domain, and would cause there to be a separate
  ready queue for each domain, the overridden mx_list causes
  the site_name to be eg: `mx_list:[104.47.24.36],[104.47.25.36]`.
  That same site_name will be used for every domain that shares those
  same IP addresses
* When `get_egress_path_config` is called to get shaping parameters,
  it is passed the routing domain `outlook.ip_rollup`. You can use that
  name with mx_rollup=false as the key in your shaping.toml, of if you
  are directly implementing `get_egress_path_config`, you can use that
  name to determine the appropriate configuration.

```lua
kumo.on('get_queue_config', function(domain, tenant, campaign, routing_domain)
  local params = {}
  rollup.apply_ip_rollup_to_queue_config(domain, routing_domain, params
  return kumo.make_queue_config(params)
end)

kumo.on('smtp_server_message_received', function(msg)
  rollup.reroute_using_ip_rollup(msg, {
    ['.mail.protection.outlook.com.'] = 'outlook.ip_rollup',
  })
end)
```

In your shaping.toml:

```toml
["outlook.ip_rollup"]
mx_rollup = false
 # shaping parameters here
```

Caveats:

* With this technique, we'll never try to use any of the lower
  priority/higher preference value MX records for any of the matching
  domains.
* The IP addresses to which the MX host names resolve can vary over time.
  We'll still queue the mail to the same scheduled queue (eg:
  `foo.com!outlook.ip_rollup`), but it's possible for there to be
  multiple ready queues with different names based on those changed
  IPs.  This is actually a feature: if the destination domain has
  an outage and are now publishing different IPs, we'll pick those up
  and use them.
* Since the ready queue names look like `mx_list:[104.47.24.36],[104.47.25.36]`
  it can be hard to intuit just from glancing at that name where those queues go.

2023-08-12 06:52:39 -07:00