By default, public-inbox-mda does some simple checks before invoking spamc(1) since it is intended to receive mail before it goes to a mailing list.
However, some users prefer to use public-inbox-mda to mirror mailing lists. This option exists to support those users.
Using this option, the following prechecks are disabled:
* multiple Message-IDs
* non-existent Message-IDs
* Message-IDs longer than 244 characters long
* From: header shorter than 3 characters
* Subject: header shorter than 2 characters
* unusable Date: headers
* inbox address specified in To: or Cc: header