How to fix? E-mails sometimes cannot be deleted and they keep showing on the notification center as well as on the e-mail icon.

Hello,

Since I updated my iPhone 5S to IOS 9, my e-mails sometimes cannot be deleted and it keeps showing on the notification center and also on the mail icon (I don't use other e-mail apps, just the mail from Apple). I can only delete them if I turn off the phone and turn on again. Someone told me that it might be because of the mail configuration, which is, imap, but I'm not sure.

Does anyone know how to fix it?? It keeps bothering me because sometimes I want to see my latest notifications, but them I have to scroll down or up all the e-mails to finally see the new notifications.

My phone is currently on 9.0.2.