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Not all email archiving solutions capture every email, but that might not be desired. In some environments, only messages sent or received from the outside world need to be retained, so an email archive that uses a gateway approach would be acceptable. But many organizations require a more complete set of email messages, so the archive must interact with the mail server to ensure that all messages, both internal and external, are retained.
Even if an email archiving application captures inside and outside messages, some messages may still fall through the cracks. Archives that "sweep" through the mail system on a scheduled basis can miss messages that are sent, received and deleted between sweeps. Since every message has both a sender and a recipient, both of them would have to delete the message (and potentially empty their trash folder) to hide a message in this way, which is often called a "double delete" scenario. Organizations that are focused on compliance must ensure that their email archive captures every message.
Many organizations would like their email archive to include messages that existed before the archiving application was installed. These messages typically come from the mail system itself, which might include a decade or more of old mail, as well as from offline or user-created archives, like the PST files created by Microsoft's Outlook mail client. Many archiving programs are able to pull in these old messages, but some can't (see "PST indigestion," below).
This was first published in June 2008