When I use the Archive or AutoArchive features in Outlook, items do not archive as expected.

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Outlook does not archive as expected because the date that is used to determine when an item is archived depends on the type of item.

Item type Archive date
E-mail message The sent or received date, or the last modification date and time, whichever is later.
Appointment The appointment date or the last modification date and time, whichever is later.
Task The completion date or the last modification date and time. Tasks that are not marked complete are not AutoArchived. Tasks assigned to others are archived only if they are marked complete.
Note The last modification date and time.
Journal entry The date the journal entry was created or the last modification date and time.
Contact Not archived.

The following actions will change the mail message's modified date/time: Forwarding, Replying, Replying to All, Editing, Saving, Moving, and Copying.

Copying or moving the message to another message folder does not always change the modification date/time; if the destination folder is a Personal Folders file (.pst), the modification date/time does not change. If the destination folder is an Exchange Server Mailbox or an Offline Folders file (.ost), the modification date/time does change.


To determine the latest modification date/time of a Mail message, follow these steps:

Step1) Choose from the View menu > Current View > Customize Current View.
Step2) Click Fields and in the "Select available fields from" list, click "All Mail fields."
Step3) Under Available Fields, click Modified, and then click Add to place the Modified field in the "Show these fields in this order" list.
Step4) Click Move Up or Move Down to position the Modified field then click OK twice.

The modified date/time for each message now appears in the Messages view.

Reference:

Microsoft