There are circumstances where this isn't necessarily true. The IRS may give the users a very small mailbox on the server with a short retention policy. To save older and more email, the user would have to archive to pst files on their local hard drive.
Being from an I.T. background, there is NO company, that I know of, nor have ever worked for, that does not archive e-mails to tape for damn near forever...per regulation.
Now, that could be the biz I work in (finance, and now gov’t), but what biz wouldn’t CYA by using cheap tape and/or media when the regulators/etc. come knocking, or from some B.S. harassment lawsuit, or...
Still, they did not (yeah, just THIS time) follow their own regs/Law in RE: computer/HDD failure. Where’s the grilling of the I.T. and the subpena of chain-of-command. SOMEONE had to sign-off of destruction, rebuild, restore, etc. Wasn’t Keebler elves coming in to save the day.