Out of curiosity, do these messages ever do anything other than potentially fill up a government official's spam filter? Not trying to troll here, just genuinely curious about these letters' impact.
My understanding is that one of the jobs of congressional staffers involves sorting and analyzing these sorts of messages.
I can't say whether or not these messages actually influence how the politician votes on the issue, but the last time I had EFF submit one of these on my behalf, I received a response back from my senator. So, someone at least reads them.
I work for Popvox and they have the same system setup. I know for a fact staffers get this information along with other reports and it isn't spam.