How exactly is it ""not working"?
Does calibre create the task? Does the mail get sent through google?
You will need to authorize your email address at
http://amzn.com/myk
Try using the test email option from the email setup in calibre, to make sure calibre can correctly send an email through your email account. If it doesn't work, post the error message you get AND MAKE SURE TO REMOVE YOUR EMAIL ADDRESS/PASSWORD.