I'm not willing to answer the challenge, but I definitely believe it could be done. If someone was willing to purchase a large list of harvested e-mail addresses and sha1sum them all, it is very likely a commonly used address would show up in it. Now, if the address you used above is actually some single-purpose address similar to what I use for all my online accounts, that would not work, but I believe that very few people use dynamic partial addresses in that way. Not even the simple ones that gmail provides.