List Spam Filtering

[Rich Kulawiec]

On Wed, May 15, 2013 at 12:18:18PM +1000, Da Rock wrote:
> I'm a big fan of _not_ having to subscribe to a list to get a quick
> hand with a one off problem (obviously not this one!)- otherwise too
> many lists get subscribed to, oodles of messages come in which you
> can't do anything about and so forth (so its not simply just a
> matter of subscribe, unsubscribe as noted).

I concur with you, which is why point #2 in my message (which I've 
elided for brevity here) comes into play: if the list-owners set
the "subscribers only" flag in Mailman, then messages from nonsubscribers
will be held for their attention.  I don't think it's unreasonable
or particularly burdensome to request that they check that queue
once a day or so, and decide how to dispose of those messages.

I should also expand on that to mention that Mailman offers a number
of choices on how that disposition is handled: list-owners can choose,
for example, to add the address in question to a list of non-subscribers
permitted to post, so that subsequent traffic from the same person
won't be held up and require attention.  I've found this quite useful
for cases where interested individuals send traffic sporadically.
I've also found it quite useful to note the email addresses of
obvious spammers and block them at the MTA, because they'll often
step through *all* the mailing lists sequentially and it becomes
tedious to discard the same spam over and over.  Blocking at the MTA
alleviates this problem.

Another way to put it is that while using this method involves a
small initial effort, it has the significant advantage of not requiring
any action on the part of legitimate message senders, and the effort
required by list-owners diminishes over time.  It also doesn't require
any coding effort or external plumbing.

> Aside from all that, the last suggestion (4) should be possible
> using some simple filtering without the need to change the
> subscription parameters. It could be possible to even do it
> automatically saving further work on a list-owner.

I urge caution on that: oh, it's a fine idea, but introducing
automation into that process has its issues/risks.  In practice,
I've found (having run many mailing lists over many years) that
the manual workload is so small that it's not worth automating.

Since I've now opened my big mouth on this topic twice: if the
list-owners are paying attention and wish assistance with this,
I'm certainly willing to help out.

---rsk