17. A non-transitory computer readable storage medium comprising program instructions executable to: obtain a copy of an electronic communication, wherein the electronic communication comprises a reference to a document, and contents of the document are not included in the copy of the electronic communication as an attachment; obtain a copy of the document, in response to the reference, wherein the document exists at a location identified by the reference; archive the copy of the electronic communication and the copy of the document in archive media; store relationship information to identify a relationship between the electronic communication and the document; and add information associated with the document to a set of archival metadata to indicate that the copy of the document has been archived, wherein the information associated with the document comprises location information which identifies the location of the copy of the electronic communication and the copy of the document in the archive media.
18. The non-transitory computer readable storage medium of claim 17 , wherein the program instructions are further executable to: detect that another copy of the document is to be archived; and search the archival metadata to determine that the copy of the document has already been stored in the archive media.