We're trying to get some Google reviews for a company by contacting their past clients and asking them to leave reviews. The process is substantially easier if they already have a Google+ account. Is there an easy way to search by email to see if they have an account?
I looked both in the Gmail API and Google+ API and didn't seem to find something.
But I remember working with the Google Apps for Business Contacts API and remembered that if I added to the contacts using the API, and added just the email addresses Google Apps filled the photo and the name for those that had Google+ accounts, maybe you can start from there.
I found this tip. The concept is sound.
We are planning to use this.