[RKDinOKC]

Since she was running a private server the users probably had accounts on her server so senders and/or recipients would not have emails from that server on any another servers. Also that way message retention policies could be put in place that would keep the messages on the server and not be allowed to store copies on the client's computer. No off-line retention of messages. These same retention policies can also be used to basically delete all the emails if you so desired.

You can also use retention policies to archive messages without any of the users knowing. Especially deleted emails. Only the top level administrator would know or have access to those archived emails unless the administrator gave access to another user. This is most likely why she had her own servers instead of using a service. A service would have top level access.

Retention and archiving policies are specifically to archive and recover messages to use in litigation. There is no reason why you couldn't use the same retention rules to make the server delete those messages. It just wouldn't be legal if your company was required to have archived messages. Probably why she had a personal server, it would not be required to provide legal access to messages for litigation.

The default install of an exchange server when you delete and email it stays in your deleted items folder for 14 days. Then it deleted from your client and no longer visible in your client. The server marks the message for deletion and holds it for 30 days. After 30 days it deletes it from the message store to save space in the message store/database.

Almost all operating systems now have a secure delete that writes zeros where the files was instead of just marking the space a usable again. There is also hard disk maintenance software that will defragment, or group the currently used files together and write zeros on the unused space.