[1] In the case of an e-mail server, single-instance storage would mean that a single copy of a message is held within its database while individual mailboxes access the content through a reference pointer.
However, there is a common misconception that the primary benefit of single-instance storage in mail servers is a reduction in disk space requirements.
The truth is that its primary benefit is to greatly enhance delivery efficiency of messages sent to large distribution lists.
In a mail server scenario disk space savings from single-instance storage are transient and drop off very quickly over time.
[citation needed] When used in conjunction with backup software, single-instance storage can reduce the quantity of archive media required since it avoids storing duplicate copies of the same file.
[3] Microsoft states that "SIS works by searching a hard disk volume to identify duplicate files.