There's an email circulating within GMail asking for your personal details if you'd like to continue using Gmail. Needless to say, don't send your details! The recipient's name is simply stated as "GMail" and the email address is not shown by default. One sure way to see if this is from a legitimate source is by looking at its email address.
To see the sender's email address (in case you don't know it yet): I encircled "hide details". This originally displays as "show details". Just click on this to toggle.
For anything related to email and internet correspondence, be wary of anything that asks for personal details or login details.
Don't they have anything better to do?