Mark unread aol emails “mark as read” and they come back as unread.

Ok so I have had iPhone since their first series and have had an aol email (I know, don’t judge me) since the dawn of email. I also have a gmail both linked to my iPhone (now 6s) When I edit my emails to “mark all as read” it will mark them all immediately but my aol emails “come back” as unread. I have tried several “fixes” such as deleting profile and re entering to “marking all as unread and then marking as read” that worked for about 5 minutes. It’s not a huge deal but it’s an easy fix for APPLE. So I know I have a dinosaur email, APPLE but give a girl some grace. Fix this plllleeeeaaaase :)) and thank you! ;)