I think this is a policy enforced on your Exchange account. I don't think this is a setting on your phone or has anything to do with data transfer or memory consumption (at least as far as your device is concerned). 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. Just because the older mails are there on disk, it will not increase memory consumption. To preserve memory consumption that in turn would leave your device slow and inefficient. Why would keeping older mails cause large transfer of data? The older mails are already downloaded and are there on your phone. To prevent large transfers of data that end up using the device communication thus leading to a faster battery drain However I don't think the accepted answer there is relevant here. There is an earlier question which is similar - Why does stock email app only keep 25 latest emails? Is there a way to make not delete the local copy of older emails?

The Tuesday email which was already downloaded and read is no longer visible?

On Saturdays, I can only from Wednesday on.

on Friday, I can see mails from Tuesday on. However, why does it not keep older mails which are already downloaded? i.e. I have set Exchange ActiveSync to download past 3 days.

Download ms active sync