Check the configuration for your mailing lists
Some mailing list software permits people to query the list server to get all the addresses subscribed to a particular list. This, as you can imagine, is like hitting the jackpot for spammers. Good software can, however, be set up so that only those who subscribe to the list can see who else is subscribed—ask the list owner to do that. Since spammers do sometimes subscribe to lists to get around that, an even better option is to set your own preferences on the list so that nobody but the list owner can see that you are subscribed by doing such a query.
Keep your messages out of list archives
Some email programs, like Eudora, can be configured to add an extra header to all outgoing messages that reads: Restrict: no-external-archive
That keeps your messages from being archived for some lists. Because spammers have been known to go through list archives to harvest addresses, that may be desirable. The downside, though, is that some people only read the web-based message archives for lists hosted by Yahoo!Groups and similar organizations, and they won’t ever be able to see your messages.
Consider using separate email addresses for each list.
If you own a domain, that’s very easy to do, and it makes it easy to filter the messages for each list to their own folder for easy reading, too. So, for instance, I might use listmail@mydomain as a basic mailing list address, then use listmail-stitching@mydomain for a cross-stitch list, listmail-filk@mydomian for a filk music list, and so on. Why do that? Because occasionally, someone will harvest email addresses from mailing lists, and if you start getting spam at a particular mailing list’s address, you’ll know where it happened. You can simply change the address for that one list (after notifying the list owner that she has a problem) and you will soon be spamfree and enjoying the list again.