Anything possible to get rid of or reduce spam mail to a Mailman list?

Dear Mailman users, list members.
Please, take a brief technical look at this page: http://european.rainbowgathering.eu/ This week, I will update this page and the rest of the website RainbowGathering.eu. Via the page european.rainbowgathering.eu, it is possible to subscribe after a few clicks to a forum that runs on Mailman 2.1.12. http://european.rainbowgathering.eu/#Forum >>> http://lists.rainbowgathering.eu/mailman/listinfo/european
Given the fact that I have planned to thoroughly update RainbowGathering.eu, I am wondering what I can do to deviate spam bots from the mailing list. Is there any measure I can take with respect to: certain HTML/CSS codes at the website? settings inside mailman?
I really would appreciate your feedback.
Respectfully yours, Bas Roufs.
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Bas G. Roufs MA
Van 't Hoffstraat 1; NL - 3514 VT Utrecht
E. BasRoufs@gmail.com; Mob. +31 6 446 835 10; Tel. +31 30 785 20 40.
Open source OS: Kubuntu 12.10, see kubuntu.org . Websites in construction: BasRoufs.eu ; Viaconsensus.nl; RainbowGathering.eu .
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Bas Roufs