Using Classic Outlook on Windows for personal email, calendar, and contact management
Create a new PST and move a small test batch into it; if that succeeds, split the 30-GB archive into smaller PST files, then repair the original PST before moving anything else into it.
A 30-GB PST is below Outlook’s default 50-GB maximum, so size alone does not establish that the file has reached its limit. However, Microsoft documents increasing pauses and unreliable performance during move/delete operations with large Outlook data files. Raising the registry limit is therefore not the appropriate first fix.^1^
1. Protect and recover the affected messages
- Do not empty the Live.com Deleted Items folder.
- Move the affected messages back to a normal Live.com folder such as Inbox, or copy them there temporarily.
- If any are no longer visible:
- Open Deleted Items.
- Select Recover items recently removed from this folder.
- Select the messages, then choose Restore Selected Items.^2^
2. Create and test a new archive PST
In classic Outlook:
- Select New Items > More Items > Outlook Data File.
- Give it a descriptive name, such as
Archive-2026.pst, and select OK.^3^ - Create one test folder in the new PST.
- Copy, rather than move, two or three noncritical messages into it.
- Open those copied messages from the new folder, close and restart Outlook, and confirm they remain there.
- If the test succeeds, create several PSTs—for example, one per year or major project—and copy folders from the original archive in manageable batches.
- Verify each batch before deleting its original copy.
This avoids placing more data into the existing large file and preserves a source copy during migration.
3. Repair the original 30-GB PST
Corruption has not been established, but the unexpected move result is sufficient reason to scan the archive after securing the messages.
- In Outlook, select File > Account Settings > Account Settings > Data Files.
- Note the path of the 30-GB PST.
- Exit Outlook completely.
- Make a separate backup copy of the PST. Microsoft recommends backing it up before repair.^4^
- Locate and run
SCANPST.EXE. A common Microsoft 365/Office 16 installation location is:C:\Program Files (x86)\Microsoft Office\root\Office16 - Select Browse, choose the affected PST, and select Start.
- If errors are found, select Repair. Keep the option to create a backup enabled.
- Run the scan again if necessary, until it reports no further errors.
- Reopen Outlook and inspect Recovered Personal Folders or Lost and Found if either appears; recovered items that could not be returned to their original folders may be placed there.^4^
4. Reduce the old PST after migration
After confirming that copied folders are complete:
- Remove the migrated copies from the old PST and empty that PST’s own Deleted Items folder.
- Select File > Account Settings > Account Settings > Data Files.
- Select the old PST, then Settings > Compact Now.
Outlook can compact automatically when sufficient unused space exists, but Compact Now starts it immediately.^5^
Do not raise MaxLargeFileSize or WarnLargeFileSize to work around this behavior. Microsoft documents a 50-GB default maximum and a 47.5-GB warning threshold for Unicode PST files, and notes that increasing the limits can reduce performance.^6^
If the same behavior occurs with the new PST
That points away from the old archive itself. Start Outlook in Safe Mode by pressing Windows+R, entering outlook.exe /safe, and testing another copy into the new PST. Safe Mode disables Outlook add-ins; if the issue disappears, disable nonessential COM add-ins under File > Options > Add-ins > Manage: COM Add-ins > Go.^7^
If it also fails in Safe Mode, create a fresh Outlook profile through Control Panel > User Accounts > Mail > Show Profiles > Add, add the Live.com account, attach only the new test PST, and retest.^8^
References
- How to troubleshoot performance issues in Outlook | Microsoft Support
- Older emails past 2 days are missing from my inbox in Outlook. Need to restore them. - Microsoft Q&A
- Create an Outlook Data File (.pst) to save your information | Microsoft Support
- Repair Outlook Data Files (.pst and .ost) | Microsoft Support
- Reduce the size of your mailbox and Outlook Data Files (.pst and .ost) | Microsoft Support
- Configure the size limit for both .pst and .ost files in Outlook
- [Classic Outlook](https://support.microsoft.com/outlook/i-can-t-send-or-receive-messages-in-outlook#repair-your-classic-outlook-program)
- Classic Outlook not responding, stuck at "Processing," stopped working, or freezes | Microsoft Support