An IMAP/SMTP based, trivial discussion list

By Cathal Garvey, Copyright 2016, Released under the GNU AGPLv3 or later.

I love discussion lists as a way to pull together communities. I used to use Google Groups for this, back when I was naive enough to think they respected my rights as a human being.

Since GoogleGroups and Yahoo offered such great free hosting for so long, it turns out the ecosystem of Discussion List hosting providers is quite narrow now. Like RSS, an anticompetitive free offering destroyed the ecosystem.

Wanting to set up discussion lists, but unwilling to host on unfriendly shores, I was left with seemingly only one option; set up a VPS or home server and run GNU Mailman and an entire email stack, plus a domain name to match, and deal with all the grief that accrues to that due to misguided spam blacklisting and other blights upon the email system.

I'd often been puzzled as to why no options exist for running Discussion lists over IMAP/SMTP, common protocols available on almost all hosted email providers. I can create IMAP/SMTP accounts for my domains on Shared Hosting with 1984 Hosting, trivially, so if I could only use those to host discussion lists I'd have no problems.

So, I decided to write my own, and listless was created.

Right now, listless barely works. I'm working on it. The base feature set right now is:

• Configuration in lua, being as simple as a set of Option = value pairs, or as complex as a fully blown script with os calls to execute local commands. See "sample_config.lua"
• An event loop for incoming mail (over IMAP) that's scripted in Lua
  • Where the event loop receives a parsed form of incoming mail
  • Where the event loop receives the local database as an object to update or query.
  • Where the event loop can also execute local commands, leveraging the full (though hazardous!) power of lua's io and os modules.
• A local database management system that accepts Lua scripts, allowing arbitrary local modifications by script. Want to load in a huge CSV of subscribers? Just write or borrow a lua script for that. Want to fetch new subscribers from a HTTP resource? Shell out to wget.
• Pretty-ish logging with categorisation (incomplete, set LOG environment variable to * to enable, like LOG=* listless my_conf.lua)

1. Get or create an email account that supports IMAP/SMTP. I use my shared hosting account at 1984hosting.com, who are awesome by the way.
2. Create a configuration file like the one in "sample_config.lua" containing your account details, and editing details like "SubjectTag" in the Constants table to your liking.
3. Create or copy/modify a lua script containing a function named eventLoop which receives as arguments config, database, message. The one given in default_eventloop.lua is a simple members-only mailing list which prepends message subjects with the "SubjectTag" string, if given. Reference this eventLoop script in your Configuration file. Notice: As attractive as the idea may at times appear, do not ever write an eventLoop that executes remote code. Email "from" headers are trivially forged, so anyone will be able to execute code. At present, the lua io, os and debug libraries are all enabled.. Don't do it!
4. Add some subscribers; Right now, this requires executing a lua script (via-mail moderator commands are a planned feature!)
   • Create a lua script similar to sample_setup.lua; see that file for inline documentation of how to use the database object to create and add subscribers.
   • Execute your file in the context of the configuration file: ./listless my_config.lua my_setup.lua
5. Initiate the DeliveryLoop, which will iterate through incoming mail and execute eventLoop for each incoming email: listless loop my_config.lua (Or, if you want logs: LOG=* loop my_config.lua)
6. Try sending some email!

• Real documentation of the Lua API.
• Limited, somewhat more secure Lua scripting over email by moderators. See relevant issue for thoughts on "console threads" idea.
• More granular access control API added to the Lua runtime for the event loop, so that less freeform lists can be hacked up easily.
• Search functions for the archive.