I am stuck there too. I'm almost certain it requires sending an email to a gmail address, but I'm not sure what that address is. I've already tried:
No response:
3.243f6a8885a@gmail.com (hexadecimal representation of pi to 11 digits)
3.243f6a8885a3@gmail.com (hexadecimal representation of pi to 12 digits)
182d4454fb210940@gmail.com (IEEE double precision representation of pi, little endian)
Address not found:
3.14159265359@gmail.com
pi@gmail.com
ea2e4454fb210940@gmail.com (IEEE double precision representation of 3.14159265359, little endian)
3.243f6a88876@gmail.com (hexadecimal representation of 3.14159265359, no rounding)
3.243f6a88877@gmail.com (hexadecimal representation of 3.14159265359, rounding)
332E3134313539323635333539@gmail.com (ASCII string 3.14159265359 in hexadecimal form)
7069@gmail.com ('p' and 'i' ascii codes to hex)
But I'm starting to think maybe my idea of using the hexadecimal representation of pi is a red herring. I also hope I'm not hitting gmail's spam filters.