Use this powershell code to apply an activesync policy to all exchange users:
Get-Mailbox -resultsize unlimited | Set-CASMailbox -ActiveSyncMailboxPolicy(Get-ActiveSyncMailboxPolicy “Policy Name”).Identity
To apply to a particular user:
set-casmailbox username -ActiveSyncMailboxPolicy(Get-ActiveSyncMailboxPolicy “Enterprise Exchange ActiveSync Policy”).identity
Ex-Shell 