Retention date calculation
Date calculation is a very important part of the work the MFA
does when it processes items. The MFA has to understand the date that
should be used to calculate the age of the item (when the item first
appears in the mailbox) and either the date when the item will expire
or the date when the MFA has to take the action the retention policy
requires (deleting the item or moving it into the archive).
Given
the nature of email, most items enter a mailbox when they are delivered
in the Inbox or are sent and stored in Sent Items. Items often stay in
these folders for much of their lifetime and, if they do stay, will
probably come under the control of either a folder tag (if defined for
the folder) or a default tag (that applies to untagged items in the
mailbox). The exception, of course, occurs when a user explicitly
applies a personal tag to an item in the Inbox or Sent Items.
When
the MFA runs, it examines items in the mailbox and determines what
processing is required. Assume that an Inbox item exists that was
delivered on 1 April 2013 and that a folder tag that requires items to
be deleted and allow recovery after 30 days is applied to the Inbox.
MFA stamps this item with a start date of 1 April 2013 by updating the
PR_START_DATE_ETC property. It then calculates the expiration date by
adding 30 days to the start date; 1 May 2013 is the result. This date
is then stamped on the item by updating the PR_RETENTION_DATE property.
On or after 1 May 2013, the MFA returns to the item and discovers that
its retention period has expired. (If you view the item by using
Outlook before the MFA returns, you’ll see the item marked as Expired.)
When the MFA processes an expired item, it takes the retention action
defined in the tag. In this case, it moves the item into the
Recoverable Items folder, where it will remain until the retention
period for the mailbox expires, at which time the MFA will remove the
item permanently from the database.
This is the simplest kind of
processing the MFA is called on to perform, but it happens for a large
percentage of items because many users leave messages in the Inbox and
Sent Items folders. People who let items accumulate in these folders
are often called pilers because they create piles of messages and then
rely on client search facilities to locate specific items when required.
Broadly
speaking, the other kind of user behavior is represented by the filers,
or people who move items from the Inbox and Sent Items into more
appropriate folders in which the items form collections that represent
important categories of work (or play) as viewed by the user. Or indeed
the user attempts to keep the Inbox and other folders under some form
of control by deleting unwanted items on a regular basis.
Assume
that your user receives a message, reads it, and then comes back to the
message a week or so later when its content is no longer required,
perhaps because he has acted on a request that was contained in the
message. Because the item has been in the mailbox for more than a day,
the MFA should have already processed it and stamped its properties
with a start and an end date for retention purposes. The user now
deletes the message as part of his cleanup effort, and the client moves
the item into the Deleted Items folder.
You now have a different
retention context because the item has moved out of the sphere of
control exerted by the folder tag placed on the Inbox. Retention
policies usually include a folder tag to control the Deleted Items
folder and, if so, the MFA now must apply the instructions contained in
that tag. Otherwise, the MFA will apply the instructions contained in
the default tag.
Assume
that the folder tag assigned to Deleted Items requires items to be
removed from this folder (using Delete And Allow Recovery) after seven
days. The MFA examines the item and discovers that its start date is 1
April 2013 and that it should now be removed on 8 April 2013. If the
user moved the item into Deleted Items before 8 April 2013, the item is
kept until 8 April 2013 and then removed. However, if the MFA processes
the items on 8 April 2013 or after, it knows that the expiration date
for the item is already past and therefore immediately executes the
retention action and moves the item into the Recoverable Items folder,
where it will remain until the deleted items retention period specified
for the database elapses. The default deleted items retention period
for newly created databases on an Exchange 2013 server is 60 days.
However, this period is calculated based on the item’s deletion date
rather than its creation date, so it will be held for another 60 days
to allow the user to recover the item during this period. (For example,
if an item is deleted on 2 April 2013, the MFA will purge it on 1 June
2013.) Some companies use an extended deleted items retention period of
up to a year to ensure that users can recover deleted items themselves
without involving administrators, a useful practice that costs a little
more disk space for databases while releasing administrators from the
tedium of having to restore databases to recover a now-important item
deleted some months in the past.
Calendar and task items pose
some particular difficulties for the MFA when it comes to calculating
their expiration date, which is why Microsoft took some time to find
the best way for the MFA to proceed and implemented only the processing
from Exchange 2010 SP2 RU4. Calendar items are either nonrecurring or
recurring and will be either in the Calendar folder or in Deleted
Items. It is possible that calendar items might turn up in other
folders, but this happens very rarely in practice; if it does, the MFA
deals with these items as if they are in the Calendar folder. The
following rules are observed:
Nonrecurring
items in the Calendar folder expire according to the end date of the
appointment or meeting. For example, if you create a calendar entry for
a trip that lasts from 1 June 2013 to 10 June 2013 and the folder tag
for the Calendar folder specifies a retention period of two years, the
item will expire on 10 June 2015.
Recurring
items in the Calendar folder expire according to the end date of their
last occurrence. For example, if a series of meetings is scheduled from
1 May 2013 to 1 September 2013, the item expires on 1 September 2015.
If a recurring event has no end date, it will never expire.
Calendar
items in the Deleted Items folder expire based on their
message-received date. If this property is not populated (for instance,
for an item the user created in his own calendar and never sent to
anyone else), the MFA bases its decision on the message-creation date.
If neither of these dates is populated, the MFA ignores the item.
Task items receive similar care when the MFA calculates their expiration. The following rules are used:
Nonrecurring
(simple one-off) tasks stored in any folder other than Deleted Items
expire based on the message-received date. If this property does not
exist, the MFA uses the message-creation date.
Recurring tasks expire based on the date of their last occurrence. A recurring task with no end date will never expire.
A
regenerating task (a special form of recurring task that generates a
specified time after the preceding instance of the task is completed;
see Figure 3) never expires. Only the most dedicated of users who understand how to make maximum use of tasks create these items!
Tasks
that have been placed in the Deleted Items folder expire based on their
message-received date. If this property does not exist, the MFA uses
the message-creation date. If neither date is available, the task never
expires.
As explained in the previous section, you can use MFCMAPI to validate the dates the MFA uses to calculate item expiration.
