This article explains how to use the Online Archive feature in Outlook to manage mailbox size. It also lists options to reduce mailbox data.
What is Online Archiving?
Online Archiving helps prevent your Outlook mailbox from reaching its storage limit. When a mailbox becomes full, you may experience problems such as:
- Being unable to send or receive new email (Mailbox full error)
- Outlook running slowly or freezing during searches
- Sync issues between Outlook and Microsoft 365
- Large mailboxes taking longer to back up or open
Online Archiving automatically moves older or less frequently used messages into a separate Online Archive mailbox stored in Microsoft 365. This keeps your main mailbox smaller and faster while ensuring older messages remain accessible when needed.
You can open and search your archived email in both the Outlook desktop app and Outlook on the web.
Learn more: Microsoft: Archive older items manually in Outlook for Windows
Apply an Archive Policy
Archive policies control when items move to your Online Archive. Review TRU requirements before choosing a policy: TRU Records Retention Policies.
Apply to your entire mailbox (recommended first):
- In Outlook, right-click your mailbox name (example: Jane Smith – jsmith@tru.ca).
- Select Properties or Data File Properties.
- Open the Policy tab.
- Under Online Archive Policy, choose a period (example: Archive items older than 1 year).
- Click Apply, then OK.
Then apply to key folders (Inbox and Sent Items):
- Right-click Inbox, select Properties, open the Policy tab.
- Choose the same Online Archive Policy, click Apply, then OK.
- Repeat for Sent Items.
Reference: Microsoft: Assign archive and retention policies
Access your Online Archive
- Outlook (desktop): The archive appears as a second mailbox under your main mailbox.
- Outlook on the web: Go to outlook.office.com and expand Folders > Archive.
Manage Mailbox Size: Quick Cleanups
Empty Deleted Items
- Right-click Deleted Items and choose Empty Folder.
- Confirm deletion.
Microsoft guide: Empty the Deleted Items folder automatically
Clear Junk Email
- Open Junk Email, remove unwanted messages.
- Right-click the folder and select Empty Folder.
Remove large or unneeded attachments
- Open the message and save the attachment to your computer or OneDrive.
- Right-click the attachment and select Remove Attachment, then save the message.
Tip: Use Search Tools > Has Attachments to find large messages quickly.
Review Sent Items
- Save large files to OneDrive or a shared location.
- Delete old or unneeded sent messages.
Additional Tips and Tools
Mailbox Cleanup tool
- Go to File > Tools > Mailbox Cleanup.
- Select View Mailbox Size to see large folders.
- Use Find items older than or Find items larger than to locate items to delete.
Microsoft guide: Reduce the size of your mailbox
Sort by size or date
Use View > View Settings > Sort, then choose Size or Received to find large or old messages.
Clean Up Conversation
- Go to Home > Clean Up.
- Choose Clean Up Conversation, Folder, or Folder & Subfolders.
Use OneDrive links instead of attachments
Share files using OneDrive links to reduce mailbox size and keep file versions current. Guide: Attach files in Outlook using OneDrive
Adjust local cache size (optional)
- Go to File > Account Settings > Account Settings.
- Select your account, choose Change.
- Move the Mail to keep offline slider to reduce local storage. This affects only local cache, not server mail.
Additional Support
For further assistance with Outlook archiving, visit Microsoft Outlook Support Page.
If you experience sign-in or TRU account-related issues, contact TRU IT Service Desk:
📧 itservicedesk@tru.ca
🔗 TRU IT Portal
📞 1-250-852-6800
📞 1-888-852-8533 (Toll-Free Canada/US)