When I first upgraded from 4.3 to 4.4 on my Samsung Galaxy S4, I noticed that while the IMAP push option for email was a truly welcome addition, email still wasn’t syncing correctly. Primarily, if I marked an email as read from another email client (desktop or web browser), it would not be marked as read on my phone,even after forcing a refresh.
One such method I’ve come across was to set the “Period to sync Email” to 2 weeks, but even this wasn’t enough. It would trigger a full update initially, yet subsequent updates still wouldn’t sync.
The fix is to make this range even shorter. I’ve noticed that 3 days seems to work well and consistently.