I've just set up some IMAP accounts in Outlook 2013 and in POP And IMAP Account Settings there is a sliding control called Mail To Keep Offline which is currently set to All.

I'm a little confused as to what this slider controls and how? Presumably it controls which emails are synced to the server but if for example I set it to 24 months does it mean that all email up to 24 months old is synced to the server or all email over 24 months old is synced to the server.

The lack of help in the product on this is not very good. 

This new feature is called Data Based Sync Slider. This allows you to limit the amount of data that is synchronized locally to your OST.  The purpose of the slider is to make Outlook usable on devices that have limited or small amounts of local storage.  ---- (1/3/6/12/All month)

If you set it to 24 months, the email up to 24 month would not sync/cache to your local OST file, all old messages would stay at server.

Cheers,
Tony Chen
Forum Support
________________________________________
Come back and mark the replies as answers if they help and unmark them if they provide no help.
If you have any feedback on our support, please contact tnmff@microsoft.com.