Spam/Abuse Resistant e-Postcard program?

[FauxCaster]

I'd like to put up a low-maintence but robust postcard program. My logs show plenty of attacks regularly for all sorts of script holes (for scripts I'm not even running). Is there a particularly secure postcard program out there? I'm considering mypostcards.com software install, but at $500+ it's a little steep, but perhaps worth it.