A suggestion...
There are many devices intended to hunt down e-mail links and slip them to spammers, which is probably what's happening in your case.
One quick and dirty fix is to eliminate the actual e-mail link, and write in plain text something along the lines of "Robert AT habitablezone.com"
The letterwriter has to tranlate it to true e-mailspeak, and type it into a letter, but it's a small hassle compared to having to sweep tons of spam off your account.