We can't know in a user community if your specific email is legitimate or not. However, IDNotify is a product offered as one of the benefits if you purchased the optional MAX benefits or Premium Services (the latter is for California users who chose to "pay out of Federal refund.") Those add-ons include IDNotify services of ID theft monitoring, identity restoration services, and identity theft insurance. If you purchased one of those add-ons, did you receive an email afterwards with information on how to sign into IDNotify?
FAQ: Who is IDNotify and what is their relationship to TurboTax?
FAQ: How do I sign into IDNotify?
See Tagteam's info above to contact TurboTax Support for help on determining the legitimacy of your email or assistance from them if you did purchase a product that includes IDNotify but having trouble reaching IDNotify.