Use this URL: http://ThisURLEnablesEmailToGetThroughOverzealousSpamFilters in your emails. It will help train statistical spam filters to count spams using that URL as non-spam, thus giving people away to avoid being erroneously filtered out by spam filters. If spammers ever start to use it, which is unlikely, they will including a link to this site, where we will educate people about fighting spam.
Essentially the idea is this. As the link gets very, very popular, spammers would want to include it in some non-clickable or invisible way on their pages.
If they start doing so, however, spam filter creators will be motivated to be update their filters so that they can differentiate between visible, clickable versions of the URL and invisible or non-clickable ones. The visible, clickable ones will become more strongly associated with real emails, and the phony ones with junk emails.
If the spammers then, out of desparation, include visible, clickable versions, they will be providing mainstream Internet users with a pointer to anti spam resources.
So it's a no-win for spammers, no matter how things evolve.
