Why does Exchange ActiveSync not keep more than 'x' days of mail?

I have a HTC Desire X. I have set Exchange ActiveSync to download past 3 days. However, why does it not keep older mails which are already downloaded? i.e. on Friday, I can see mails from Tuesday on. On Saturdays, I can only from Wednesday on. The Tuesday email which was already downloaded and read is no longer visible? **Is there a way to make not delete the local copy of older emails?** There is an earlier question which is similar - https://android.stackexchange.com/questions/28780/why-does-stock-email-app-only-keep-25-latest-emails However I don't think the accepted answer there is relevant here. From that answer > to prevent large transfers of data that end up using the device communication thus leading to a faster battery drain; Why would keeping older mails cause large transfer of data? The older mails are already downloaded and are there on your phone. > to preserve memory consumption that in turn would leave your device slow and inefficient. Just because the older mails are there on disk, it will not increase memory consumption. A better way to program it would be display '3' days but have a way to show older ones on demand - since the app would read it from disk only on demand, it wouldn't increase memory consumption. My phone runs Android 4.0.4.