Howdy folks!
I mentioned this at Tuesday's meeting, but for the benefit of those of you who weren't there, but are active on the MUUG roundtable mailing list, I thought I should repeat it here.
As of Tuesday afternoon (November 14th), I've installed a package called milter-greylist (http://hcpnet.free.fr/milter-greylist/) on the MUUG server, to help in our ongoing battle against spam. So far, it's been remarkably effective (in combination with SpamAssassin and spamass-milter, which had been previously installed) at reducing our incoming spam.
Since we've configured it to greylist all external addresses by default, this may impact some of you when you post to the list via e-mail. The first time it comes across the combination of your (or your ISP's) SMTP server IP address, your return e-mail address, and the destination e-mail address, it will temporarily reject the message, asking the SMTP server to retry again after some time (I've set that delay to 14 minutes). After that, that combination stays cached in the greylist for some amount of time (which is set by default to 5 days), during which time the same combination of addresses will be accepted without delay.
The net result of this is that you may occasionally see a delay between when you send e-mail to the list and when it actually gets received, especially if you post infrequently. Rest assured, however, that your message should get through without too much extra delay.
If for some reason you find yourself unable to send at all, you can contact me at me e-mail address below (and not the muug.mb.ca address). We're also running the same milter-greylist software on that server, but with a less aggressive policy, which does default white-listing in most cases. Preferably, contact me from exactly the same address you try to use for posting to the mailing list, so I can check e-mail headers to determine SMTP server address information, etc. I will then, if necessary, add the appropriate whitelist override for your address on the MUUG server.
For those of you running your own sendmail servers on the Internet, I highly recommend milter-greylist. It's very small, doesn't use up much CPU or memory (much, much less than SpamAssassin in both cases), and seems to work very well. (Make sure you put it first in your InputMailFilters list, so the other milters don't have to do as much work.)
If you're not running sendmail, but some other SMTP server, you should look for a similar grey-listing solution for your mail server.