This is an odd article as it misses a number of important points:
-- There's no obligation to store email for seven years or any other time. There ARE obligations for different times for different things -- payroll, contracts...
-- There's no magic cutoff at seven years. If you're holding information that's ten years old, and it's relevant, the court can order you to discover it
-- Filing system documents are just as vulnerable as email to being produced in 'discovery'
The proper approach is
-- A clear policy which is appropriate for your business (so it covers stuff you keep indefinitely, and a cut-off date for things you don't want) and isn't just wriggling to avoid legal obligations
-- Implementation of your policy -- IE you actually DO delete stuff older than eighteen months. Crucial.
-- Implementation of a 'legal hold' so stuff which is being discovered at month 17 won't be deleted before it can be produced.
Unless you can actually delete (from archive and tapes) and retain for legal holds, I would say that you're better off keeping everything, and cataloguing your tapes REALLY carefully.