E-mails sent to multiple recipients can result in identical MIME files in at least two recipient mailboxes. We refer to these as Duplicate e-mails.

Duplicate e-mails

Duplicate e-mails are MIME files delivered by the e-mail server that have identical pairs of byte sequences.

Multiple recipient e-mail

When an e-mail is sent to more than one recipient, we refer to this as a multiple recipient e-mail.

Please note: Sending an e-mail to more than one recipient can result in duplicate e-mails. It is not possible to deduce the number of duplicate e-mails from the number of multiple recipients.

Consequences

Duplicate e-mails can only be recognized using the full content of two MIME files. This means that there is no way to recognize duplicates unless you compare the content of two MD5 values. Recognizing duplicates would seem to make sense in terms of saving storage space. However, this is based on the false assumption that you can only avoid redundant storage if duplicate copies are only stored once. The correct method is to configure an MD5 path as the physical storage path, which automatically ensures that duplicate files physically exist only once. This method is called the passive duplicate check. Attempting to recognize e-mail duplicates before they are stored is an additional, unnecessary step that also reduces performance.

The message properties PidTagInternetMessageId and PidTagSearchKey provide a direct option to detect multiple recipient e-mails. The pseudo-property EloSearchKey initially tries to use PidTagInternetMessageId, and in the absence of this property, tries to find PidTagSearchKey.

Before you use these properties, you need to take note of the following:

• Determining multiple recipient e-mails is not an adequate substitute for recognizing duplicate e-mails. Pairs of multiple recipient e-mails are not always duplicate e-mails.
• The two properties not available for all Exchange items and cannot therefore be used in all cases to recognize multiple recipient e-mails.
• Identifying all mailboxes associated with a multiple recipient e-mail can also reveal BCC recipients. It is therefore necessary to consider in each scenario whether privacy regulations are being breached.