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Q249680: XADM: Deleted Item Retention and Message Delete Process

Article: Q249680
Product(s): Microsoft Exchange
Version(s): winnt:5.5
Operating System(s): 
Keyword(s): exc55
Last Modified: 06-MAY-2000

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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SUMMARY
=======

This article explains the message deletion process and the method that Exchange
Server uses to handle delete requests when the Deleted Item Retention option is
selected, to help Exchange Server administrators understand this process and
plan for this process accordingly.

MORE INFORMATION
================

Client Perspective
------------------

When a client profile is configured to store messages on the server, a message
exists in a folder, and a delete operation is requested, under normal
circumstances, the message is moved to the Deleted Items folder. When you empty
the Deleted Items folder, a request to delete the message is sent to the
Exchange Server information store. You can also force the deletion of messages
from any folder by pressing SHIFT+DELETE while the messages are selected.

If a client profile is configured to deliver to a personal folder file (.pst)
instead of to an Exchange Server mailbox, the message is actually deleted from
the Inbox folder after the message is copied to the local .pst file, instead of
being moved to the Deleted Items folder. For additional information about how to
view the contents of the dumpster that contains items that have been deleted
from folders other than the Deleted Items folder, click the article number below
to view the article in the Microsoft Knowledge Base:

  Q178630 XADM: How to Recover Items That Do Not Touch the Deleted Items Folder

Information Store Perspective
-----------------------------

When the information store receives a request to delete a message in a particular
folder referenced by the Message ID, the information store determines if the
message should be soft deleted (also referred to as logical deletion) or hard
deleted (also referred to as physical deletion). A hard deletion of a message is
performed when any of the following criteria are met:

- The client specifically requests a hard deletion.

- The effective item retention time is zero.

- The registry key that indicates "Force Hard Deletes" is enabled for the
  private or public information store.

- The account requesting the deletion is a gateway.

- The account requesting the deletion is a system.

Soft Deletion
-------------

A soft deletion is performed if none of the criteria for a hard deletion are met.
A flag is set on the entry in the MsgFolder table that indicates that the
message has been soft deleted from the folder. Message counts for the mailbox
and folder are also updated. At this point, the message is available to deleted
item recovery.

During the next scheduled information store maintenance process, each folder is
examined to determine if any of the soft-deleted messages that the folder
contains have passed the deleted item retention time. The deleted item retention
time for the private and public information store is configured in the Exchange
Server Administrator program. If such a message is found, the message is hard
deleted. For more information about hard deletion, see the "Hard Deletion"
section of this article. You can also control information store maintenance
scheduling by using the Exchange Server Administrator program.

For additional information about how to configure deleted item retention, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q246283 XADM: Set Deleted Mail Message Retention Time in Exchange Server 5.5

For additional information about information store maintenance and scheduling,
click the article number below to view the article in the Microsoft Knowledge
Base:

  Q159196 XADM: Tasks Controlled by the IS Maintenance Schedule

Hard Deletion
-------------

When a message is hard deleted, the message reference is immediately removed from
the MsgFolder table, which is a mapping between entries in the folder table and
the messages table. At this point, the message is no longer available to the
mailbox that contains the folder, even if you use deleted item recovery. The
reference count of the message is checked. When the message reference count
drops to zero, which means that no other mailbox has a copy of the message, an
entry is made in the DeletedMessages Table that indicates that the message is
ready to be removed from the messages table.

During the next background cleanup process, the entries in the DeletedMessages
table are examined and the corresponding entries in the messages table are
deleted. This process occurs every hour by default, but you can control this
schedule by editing the following registry entries:

- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS
  \ParametersPublic\Background Cleanup (value in milliseconds)

- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\
  ParametersPrivate\Background Cleanup (value in milliseconds)

For additional information about the background cleanup process, click the
article number below to view the article in the Microsoft Knowledge Base:

  Q159306 XADM: IS Maintenance Tasks Not on IS Schedule

Conclusion
----------

If you enable and increase the deleted item retention time, you may need to
perform additional capacity planning. The following example demonstrates that
messages can be present for an extended duration even after the messages have
been deleted by the user:

- Deleted item retention is set for 48 hours.

- Information store maintenance is set to run between 3:00 A.M. and 7:00 A.M.

- Background cleanup is configured to run every hour.

In this example, if you delete a message at 8:00 A.M., the message does not
become a candidate for hard deletion for 48 hours. The next information store
maintenance procedure is scheduled to finish at 6 A.M., so the message is not
hard deleted (the record is not removed) for 71 hours.

Additional query words:

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Keywords          : exc55 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : winnt:5.5
Issue type        : kbinfo

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