The policy is to delete all e-mails after 30 days, unless they are stored in 
a folder. E-mails stored in a folder are erased after one year. The policy 
has many benefits. First it clears up computer storage space.
The policy can  also results in signifigant cost savings in litigation where 
a Judge has required the wholesale production of  e-mails. Imagine if we were 
required to sift through and digest 12-24 months of e-mail traffic. This has 
happened to a number of companies in litigation  the US( who have 
subsequently changed their retention policies). Frankly, the Microsoft  
antitrust case opened a lot of eyes to the dangers of not having a policy. In 
that case, the discovery by the Dept of Justice produced some very damaging 
e-mails that were later used to effectively cross-examine Bill Gates and 
others. It is unbelievable  what some people will put in an e-mail that they 
would never dream of putting in a "written"  document.
As for your comment about the subsequent retrieval of deleted e-mails, I (and 
Bob) have been told many times that a deleted e-mail cannot be retrieved. 
Please check with your source. I am happy to discuss any questions you have 
about the policy.