Go to Settings and accounts and choose your Exchange account:
Here you can configure 2 things:
1. Days to sync: days back you want to sync with the server. I.e. - how many days / weeks ( time) would you like to upload to the mail client. The more you go back in time to retrieve emails - the longer it will take to sync and the more battery resources it will take. Keep that in mind. Please note that this option only pertains to the default setting for new folders. for existing folders you will need to change the setting manually (below).
2. Inbox check frequency: how often shall the application check for new incoming mails. This is a general configuration for the account Inbox and Sent Items only.
3. Sync period for existing folders: In order to configure sync for existing folders (including your inbox) - go to each folder and from the folder open "Menu" and go to "Sync options". Those settings will affect ONLY that particular folder sync settings. Non-inbox folders that will not have a manually defined sync period configured - will not be automatically synced.
(for non inbox folders) Check the "Sync this folder" check-box:
And then press on "Days to sync" to define the time to sync back to: