Google is introducing a new feature which will allow you to email someone where you will not have to know the email address. Regarding this feature, I would like to post How you can stop any one mailing you.
You Can go to your Gmail Settings and Find “Email via Google+:” and set it accordingly to Anyone, Extended Circles, Circles, or No One.
Here is the link to open Gmail settings
Now if you want to send an email to some one, and you don’t know the email address of the person, just type the name of the person and if there is a Google profile matching that data, you can send email to that person.
Your email address isn't visible to your Google+ connections until you send them an email, and their email addresses are not visible to you until they respond. They will not be allowed to send you another email unless you reply or add them to circle. But this may help spammers who can send mails to so many people who will not change the settings.
So what you think about this new feature from Google ?