This document explains step-by-step
how to: - Enable an Archive Mailbox for a user - Create Retention
Tags - Create and assign Retention Policies - Verify that emails are
moving to the archive
Use an Archive Mailbox
when: - User mailbox size is very large - Outlook OST/PST size is growing too
much - Backup of Outlook data is failing - Performance issues are reported in
Outlook
Important: Archive
mailbox is a server-side solution. It does NOT depend on the user’s
laptop.
Before starting, ensure: - Mailbox is hosted
on Microsoft 365 / Exchange Online - You have Global Admin or Exchange
Admin access - User mailbox exists and is active - You are logged in from
an admin system (not the user’s laptop)
1.
2.
Navigate to: Recipients → Mailboxes
3.
Select the required user mailbox
4.
Open Mailbox settings / Others / Mailbox
features (UI name may vary)
5.
Find Archive mailbox
6.
Click Enable and confirm
Result: Archive mailbox is
enabled for the user.
⏱ Time to appear in Outlook: 15–60
minutes
Enabling archive
alone does nothing. Retention tags tell the system when to move emails.
1.
2.
Go to: Solutions → Data lifecycle management
→ Microsoft 365 → Exchange (legacy)
3.
Click MRM Retention tags
4.
Click + New tag
·
Name: Move to Archive – 1 Year
·
Apply this tag to: Automatically to
entire mailbox
·
Retention period: 365 days
·
Retention action: Move items to archive
5.
Save the tag
Retention policies group
one or more tags and apply them to mailboxes.
1.
In
the same Exchange (legacy) section, open: MRM Retention policies
2.
Click
+ New policy
3.
Enter
policy name: Example: Archive Policy – 1 Year
4.
Click
Add tag
5.
Select
the tag created earlier (Move to Archive – 1 Year)
6.
Save
the policy
1.
2.
Navigate to: Recipients → Mailboxes
3.
Select the user mailbox
4.
Open Mailbox policies
5.
Under Retention policy, select: Archive
Policy – 1 Year
6.
Click Save
Policies run
automatically, but you can speed up archiving.
Open
PowerShell as Administrator
Connect to
Exchange Online:
Connect-Exchange Online
Run:
Start-Managed Folder Assistant -Identity user@domain.com
To reduce OST file
size:
1.
Open Outlook
2.
Go to: File → Account Settings → Account
Settings → Change
3.
Set Mail to keep offline to:
o
3 months or 6 months
4.
Save and restart Outlook
·
Archive Status shows Active
·
Retention policy assigned to mailbox
·
“Online Archive – Username” visible in Outlook
·
Old emails slowly appearing in Archive
·
Outlook performance improves
·
Archiving is not instant (24–72 hours
typical)
·
Do NOT back up OST files
·
Do NOT create PST files unless explicitly
requested
·
Always test policies on one user first
Archive mailbox + retention tags +
retention policy + reduced Outlook cache = permanent solution to Outlook
storage and backup issues.
Skipping any step results in incomplete
or failed archiving.
·
Prepared for: IT Operations / Intern Training
·
Environment: Microsoft 365 / Exchange Online
·
Usage: Production & Training