This is the second emergency update released by Microsoft for Windows 11 this month. The first one - KB5077744 - was released on January 17, 2026. However, the KB5078127 update is important because it fixes several issues.
Why the Out-of-Band Update - KB5078127 - for Windows 11 is Important?
The January 13, 2026 cumulative update for Windows 11 introduced several functional bugs and issues, including:
- Outlook Classic when using POP email accounts crashes, hangs, or shows “Not Responding” error.
- Failure to reopen the Outlook application without ending its process from the Task Manager.
- Emails in the Sent Items folder not appearing after being sent.
- Outlook re-downloading the emails.
- Issues with PST files, particularly those stored on cloud services, like OneDrive.
Owing to the severity of these issues, Microsoft released the out-of-band cumulative update - KB5078127 for Windows 11, to not only fix the Outlook-related issues but also consolidate previously released fixes.
According to Microsoft’s official notes and community forum’s discussions, the key improvements in the update include:
- Classic Outlook clients that were freezing, hanging, or crashing when accessing POP accounts are now normally functioning.
- PST corruption or sync inconsistencies are corrected and data in PST files is accessible.
- Issues such as missing items in Sent Items folder or repeatedly re-downloading old emails are corrected.
- Errors when opening or saving PST files on cloud apps, such as OneDrive or Dropbox, are now resolved.
How Install the Windows 11 KB5078127 Update?
The Windows 11 KB5078127 is an ‘out-of-band’ update that will be downloaded automatically. The update is provided through the Windows Update mechanism to the affected systems which have already installed the January 13 update.
If you’ve the “Get the latest updates as soon as they’re available” option enabled on your system, you will receive the update automatically. If not, then you can manually installed the update by going to Settings > Windows Update on your system.
What if you’re still facing issues when accessing Outlook and PST File?
According to Microsoft, the issues related to Outlook and PST files have been addressed with the Windows out of band update KB5078127. However, if you’re still facing sync issues with your Outlook POP profile and accessing PST file data, then follow the below solution:
Solution 1: Repair the PST File
If you’re facing issues when accessing PST file or the file is corrupt, then use ScanPST to repair the PST file. Here’s how to use the ScanPST:
Note: Make sure to take a backup of your PST file before running ScanPST as sometimes it results in data loss.
- Find ScanPST on your device. Double-click on it to launch it.
- Click on the Browse button to select the PST file.
- Click on Start to scan the PST file.
- Once the scanning is finished, it will list the errors found.
- Click on Repair to fix these errors.
- Once the repair process is complete, check if the issue is resolved.
Limitations of ScanPST:
- Fixes only minor corruption issues in PST file.
- Risk of data loss as the utility may delete unrecoverable items.
- Needs to be run multiple times to completely repair the PST file.
- Only fixes structural issues in PST file.
- Freezes, hangs, or even fails to repair large PST files.
To overcome the ScanPST limitations and repair the PST file without any data loss, you can opt for Stellar Repair for Outlook – a powerful PST repair software. This software can seamlessly and effectively repair severely corrupted PST files of almost any size. It restores all your mailbox items to a fresh PST file by preserving the original folder structure and hierarchy. Apart from PST, it allow to save the repaired items in formats, like HTML, EML, MSG, PDF, etc.
Solution 2: Repair or Recreate Outlook Profile
If you’re facing sync, hanging, freezing, or other issues in your Outlook, then you can repair or recreate your profile.
To repair the Outlook profile,
- In Outlook, go to File.
- Choose Account Settings > Account Settings.
- Under the Email tab, select your profile and then click the Repair option.
- Follow the prompts to complete the repair process.
When done, restart Outlook and see if the issue is resolved. If not, then recreate the Outlook profile. Here’s how:
- On your system, go to Control Panel.
- Click on User Accounts > Mails (Microsoft Outlook) > Show Profiles > Add.
- Provide a name to the new profile and click OK.
- Enter the login credentials of your account and then click Next.
- Click Finish.
Conclusion
Microsoft released the KB5078127 for Window 11 out-of-band update to address issues caused by the January 13, 2026 Patch Tuesday update. This cumulative update has fixed the Outlook POP account and PST file issues and addressed the cloud file access issues. If you’re using Classic Outlook with POP accounts and facing the issues after installing the January 13 update, then install this update immediately (if not done already) to prevent Outlook crashes and restore normal mail functionality.
In case, you’re still facing Outlook hang or crash issues, then repair or recreate the Outlook profile. If the PST is corrupt, then the best solution is to use Stellar Repair for Outlook – a powerful PST repair software. This software can repair large, highly corrupted PST files and recover all the mailbox items with complete precision and integrity.
5 min read
