This can be done a couple of different ways...
For simplicity I've outlined the per-mailbox store method. From Exchange System Manager go to:
Administrative Group-->First Admin. Group-->Server Name-->DB Name (has the yellow icon)-->Store Name (has the mailbox icon).
Right click on the store name, click Properties. Go to the 'Limits' tab and set the retention periods at the bottom of this screen. If you have multiple stores, as we do, then you can configure a per-store policy. For example, for the average users you could have a 60 day window but for your executive team store you could set a 360 day window for deleted item retention.
From this point forward you can view the deleted mailboxes in the right-hand pane through selecting the mailboxes icon.
If your information store isn't large then brick-level backups are great...in reality they're too slow for most of us.
Another alternative is to use one of MS's utilities to create a PST-based brick level backup on a quarterly basis (Yes, we'll answer if you have more Questions

). Through this you could easily retreive an individual email that's older even if it's outside your deleted item retention time-window.