[iMore Question]

Why does blue dot not disappear when I have read email on my Apple iPad air2 ?

[Ledsteplin]

Be sure you are not choosing "Mark As Unread". If you do, the blue dots come back. If that's not it, try a hard reset.
Hold the top power/sleep button and the home button at the same time until the Apple logo appears, then release.

[Just_Me_D]

Why does blue dot not disappear when I have read email on my Apple iPad air2 ?

I don't know, but you can try rebooting your iPad or login to your email account via a computer and see if there's a setting that prevent email messages being marked as read in mobile devices.