Outlook Archiving Didn’t Reduce Email Storage (IMAP Accounts)

Outlook Archiving Didn’t Reduce Email Storage (IMAP Accounts) #

If you use Outlook Classic with an IMAP email account and enable archiving (for example, “archive anything older than 6 months”), you may notice that your mailbox storage usage does not decrease.

This is expected behaviour for IMAP. In most cases, nothing is broken — it’s a common misunderstanding of how IMAP works.

Why Archiving Doesn’t Reduce IMAP Mailbox Size #

With IMAP accounts:

• Your email is stored on the mail server.
• Outlook is a sync client that displays what is on the server.
• Outlook’s Archive / AutoArchive feature typically saves a copy to a local archive file (PST).
• The original messages usually remain on the server unless they are moved out of the IMAP mailbox or deleted.

Result: Your Inbox/Sent folders on the server still contain the same email, so server mailbox storage stays the same.

Important: “Archiving” vs “Reducing Storage” #

• Archiving for organisation (moving messages into an IMAP “Archive” folder that still sits under the IMAP account) will NOT reduce storage usage — the email is still stored on the server.
• Reducing storage usage requires messages to be moved to a local (non-IMAP) location or deleted from the server.

How to Actually Reduce IMAP Mailbox Storage #

Option A (Recommended): Move Old Mail to a Local Outlook Archive (PST)

This stores old mail on the computer in an Outlook data file (PST), and removes it from the server.

1. Open Outlook Classic.
2. Go to File → Account Settings → Account Settings.
3. Open the Data Files tab and confirm you have an Outlook Data File (.pst) listed.
   • If you do not have one, click Add… and create a new PST file (e.g. Archive.pst).
4. In your Outlook folder list, locate Outlook Data File (this is local, not the IMAP account).
5. Create an archive folder under the PST (example: Archive 2024).
6. Select older emails in your IMAP folders (Inbox/Sent/etc.) and drag them into the PST archive folder.
7. Allow Outlook time to sync changes.

Tip: Mail moved into folders under Outlook Data File is stored locally and will no longer count toward your server mailbox quota.

Option B: Archive Locally, Then Delete from the Server

If Outlook has already created an archive file but storage hasn’t changed, Outlook may have archived a copy but did not remove the original messages from the IMAP mailbox.

1. Confirm your archive exists: File → Account Settings → Data Files.
2. Verify the old emails are present in your archive/PST.
3. Delete the same old emails from the IMAP folders (Inbox/Sent/etc.).
4. Empty Deleted Items (this is important).
5. Wait for Outlook to finish syncing.

Common Reasons Storage Still Doesn’t Drop #

• Emails were moved into an IMAP “Archive” folder (still stored on the server).
• Deleted Items is not emptied (messages still count until purged).
• Sent Items and other folders contain most of the mail (not just Inbox).
• Large attachments are the main cause of mailbox usage.
• Outlook hasn’t finished syncing changes yet (especially on large mailboxes).

Recommended Best Practice #

• Use IMAP for day-to-day email across multiple devices.
• If you need to reduce mailbox size, move older email into a local PST archive.
• Back up your PST file — it is stored on the local computer and is not automatically protected by the mail server.

Need Help? #

If you’re unsure whether your archived mail is stored locally or still on the server, contact support and let us know:

• Whether the account is configured as IMAP
• Which Outlook version you are using (Outlook Classic / New Outlook)
• Approximately how large the mailbox is currently using

We can help confirm the safest way to archive mail without losing anything important.