I was sent a Careers invitation by a current user about a two weeks ago. I am already a Careers user, so when I clicked on the "accept invitation", I got to a page on Careers that says:
You already have a profile! No need to accept the invitation below.
Just today, I received a reminder email letting me know that the invitation expires in 3 days. I still get the same message telling me I already have a profile.
I'm thinking that current users who get invites shouldn't get the email, as they're already users, or if they do get the email, simply navigating to the invitation page should make it so that Careers doesn't keep emailing me about an invitation that I can't really "accept" as I'm already a user.