When using IMAP email accounts in Microsoft Outlook, it is common to manage mailbox storage by deleting emails or moving them into different folders. However, after performing large operations such as deleting thousands of emails or rearranging mailbox folders, Outlook may appear stuck at the “Checking for new mail in subscribed folders…” message during Send/Receive progress.

This usually happens when Outlook is trying to re-sync the mailbox with the email server. Since IMAP maintains a complete copy of your mailbox both locally and on the server, major changes can create a large synchronization backlog.

⭐ Why This Issue Occurs

• IMAP performs two-way synchronization

• Folder structure changes must update on server

• Deleted item purge takes time

• Thousands of headers and message states need re-indexing

• Large mailbox size (e.g., 30GB or more)

This process may take several hours depending on:

✔ Internet speed
✔ PC performance
✔ Number of emails being moved
✔ Server response time

Outlook may look frozen, but it’s actually processing sync tasks in the background.

? Recommended Fix Steps

1️⃣ Allow Sync to Complete

Keep Outlook open for several hours (or overnight)
Do not restart or shut down during active sync

2️⃣ Empty Junk & Deleted Items

Reduces server workload and speeds up syncing

3️⃣ Unsubscribe Unnecessary IMAP Folders

Right-click email account → IMAP Folders → Query → Unsubscribe unused folders

4️⃣ Reset Send/Receive Groups

File → Options → Advanced → Send/Receive

5️⃣ Rebuild IMAP Database (OST file)

If Outlook remains stuck:

1. Close Outlook completely

2. Press Win + R

3. Paste and Enter:

   %localappdata%\Microsoft\Outlook\
   

4. Rename the .ost file (example: add .old)

5. Restart Outlook → mailbox will download fresh

⚠ A complete 30GB mailbox may take hours to fully rebuild.

? Pro Tip: Consider Upgrading Email Type

If your mailbox is large and Outlook is used heavily:

? Upgrade from IMAP to Exchange / Microsoft 365

Benefits of Exchange sync:

• Faster performance

• Better indexing

• No folder-by-folder sync delays

• Instant server updates

? Conclusion

This is not an error — Outlook is synchronizing major mailbox changes.
Let the process finish and follow optimization steps to avoid future delays.
If mailbox size continues to grow, consider upgrading the email solution for long-term stability and performance.

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