Archiving data

We run backups “regularly.”
A:What is the strategy used in other organisations about backing up:
1.Desktop applications
2.E-Mail
3.Draft document

B: How long is the backup kept?
1. Desktop applications
2. E-Mail
3. Draft documents

C: If the organisation is one that does major investigations and a “case” is continuing, but an email is stored as a document against that case then how is this backed up?

These are some of the frustrations I have?
Can someone help.

PS: We have just started implementing an EDMS but in a small pilot area.

Ann