TODO

- Milter support
- Ability to modify the body of email (e.g add a banner)
- Create a config file for each of the core shipping configs, so people have something as a baseline
- IMAP server (long shot for now)
- Plugins to copy from Qpsmtpd:
  - dspam
  - greylisting
  - virus/*

Outbound improvements
 - Rate Limiting (there's a branch for this but it's incomplete)
 - Provide better command line tools for manipulating/inspecting the queue
 - Add the ability to force a run on a specific queue file or destination domain
 - Make retry times configurable (handle RFC requirements for 5 days and DSN queued warnings)
 - Limit concurrency by domain
 - Disable deliveries for a domain
 - Pool connections by domain/MX

Plugin behavior changes
 - in SpamAssassin plugin, change default behavior of 'legacy' status header.
   Presently, when undefined, legacy is used. Legacy support should be changed to
   only when requested, with a sunset date.

Remove the following deprecated plugins
 - rdns.regexp
 - data.nomsgid         (subsumed into data.headers.js)
 - data.noreceived               ""
 - data.rfc5322_header_checks    ""
 - daemonize
 - mail_from.nobounces  (subsumed into bounce.js)
 - mail_from.blocklist
 - rcpt_to.blocklist
 - lookup_rdns_strict
 - mail_from.access     (replaced by access.js)
 - rcpt_to.access                 ""
 - connect.rdns_access            ""
 - relay_acl
 - relay_all
 - relay_force_routing

Rename the following plugins
 - toobusy      -> connect.toobusy
 - attachment   -> data.attachment
 - avg          -> data.avg
 - clamd        -> data.clamd
 - spamassassin -> data.spamassassin

Move the following plugins:
 - test_queue   -> queue/test_queue

Built-in HTTP server
- instead of each plugin bringing their own, and getting relegated to some
  god-forsaken port number:
- a dispatch mechanism, so each plugin gets their own URL space
- uses the same TLS/SSL certs as smtpd
- auth against SMTP-AUTH provider