Oh, that's just great, I finally get my Thunderbird, filtering nicely, and everything, rarely see spam.. it was all "Thunderbirds are Go!"... and then.. it pops in through mailing list :| Didn't see that one coming. (I have my mailing list on full mode, rather than digest, which is why I'm a tad late to the "party" :p (Personal preference)
Thankfully mailing list spam is rare :-).
As for blocking "known" spam addresses, trust me, that really does not work. Tried doing that oh, so many times with my inbox(s), in the end I just set up specific "word" filtering, which basically, if an email comes through with known common words used for spam (Such as your bank account is insecure, change your online password etc from banks I'm not even with :| Even if I was signed up with the bank, I would check the link first see where it really goes :-)) (Staying smart is the best way to not get conned ;-) )
But if you want to truly block spam, you'll need to block out all accounts from: gmail, hotmail, yahoo & any other free provider, but clearly that cannot happen for fairly obvious reasons :| Though if you don't already block out all the "temporary" 1 hour or 10 minute inbox providers then go block those ;-)
But to be honest, one spam message on the list, isn't bad, it could of actually been a "human bot" basically, a someone who actually sends spam rare now, but it still goes on :-), when it's actually people sending the spam, it's hard to block.
No need to go around rushing for spam filtering at this moment of time in my opinion, one or two messages can slip through any mailing list, heck could even slip through the "worlds most spam blocking machine" (If there is one). It happens. Also, everyone has to apply to the mailing list (I assume), which helps prevent spam on it's own. Until you guys start getting regular spam, there's nothing to worry about :-)
I'm gonna stop now, before I put you guys "asleep" :-D. Surprised you read this far though. :-D Also gotta close the window, before the snow makes my window shelf white. (Or gets into my comp) (It's snowing here :-D)
Just my 2p (Or rather, rambling on lol.)