These days, most online service providers offer linked services. Getting an account with one automatically opens accounts for you with the others.
It’s really nothing to worry about; the recipient’s email program is likely grabbing information from your profile. There may be something you can do about it, if you care.
Facebook popups asking you to share content can be annoying. There’s a reason websites do it, but the best practice is to be unobtrusive. So what can you do to get rid of those annoying popups?