Public Folder Migration Failed – A Corrupted item was encountered: Folder ACL

Public Folders work fine. But when it comes to migrate them to an Office 365 tenant, it may be a bit chaotic. Issues may arise, especially when you have large Public Folders.

In case of a hybrid setup – be it Exchange Server 2010, 2013, 2016 or 2019, following are the steps to migrate the Public Folders:

  • Download the Migration Scripts from Microsoft to run on the on-premises server.
  • Prepare for the migration by checking that there are no orphaned Public Folder objects and confirming their SMTP email address while making sure that there are no duplicates.
  • Generate CSV Files for mapping local Public Folders to online Public Folders.
  • Create Public Folder Mailboxes in Exchange Online.
  • Start the migration request by using the downloaded scripts.
  • Lockdown the Public Folder on the legacy Exchange Server so that no changes are done on them. Here is where downtime starts. And you need exclusivity of the folders to start off the migration.
  • Finalize the Public Folder migration to kick off the migration of data and synchronization of file between local and the online folders.

However, sometimes, at the last step you might end up facing the below given error.

A Corrupted item was encountered: Folder ACL
Corrupted item was encountered: Folder ACL

However, you can avoid this error by following the fixes discussed below or using an EDB to PST converter software, such as Stellar Converter for EDB. The software lets you export the mailboxes and Public Folders from Exchange database (EDB) to Office 365 in a few clicks.

How to Fix the ‘A Corrupted item was encountered: Folder ACL’ Error?

Troubleshooting this error can be of a hassle. Although the process is supported by Microsoft, it involves a good number of scripts and depends on several factors of the Exchange Server, such as it is healthy and running well. Also, there are too many points of failure which could take a while to understand where the issue is.

When migrating Public Folders to Office 365, you must also take the limits into consideration, as given below.

  • Maximum Public Folders – 250,000
  • Maximum sub-folders in a Public Folder – 10,000
  • Maximum items per folder – 1,000,000
  • Maximum Public Folder mailboxes – 1,000

You would also need to consider the size of the items. An item cannot be larger than 49 MB. During migration, large items may be skipped or the whole process may stop.

Public Folders are known to give issues, especially when they’re large-sized. Although they are still highly used, it seems that Microsoft is phasing them out when it introduced Shared Mailboxes and Microsoft Teams/ Groups. This is great, but you will end up with the dilemma on how to export the Public Folder to a PST file.

One of the solutions would be to export the Public Folder to PST and import it directly into Office 365 by using the Blob Storage for import and the XML file to start the migration. Unfortunately, you cannot use the New-MailboxExportRequest cmdlet to export Public Folder to PST. Instead, you can use the Outlook to export Public Folder to PST. For this, you need to have a dedicated resource with Microsoft Office installed.

A Corrupted item was encountered: Folder ACL

However, there are some limitations when it comes to exporting Public Folder to PST by using Outlook.

  • There is a size limit of 50 GB.
  • For large Public Folders, it is a messy situation as Outlook would not be able to handle large PST files.
  • There is no continuity if the process stops or Outlook crashes.
  • It will take ages to finish.
  • The Public Folder must be online.
  • Cannot export more than one Public Folder at once.
  • No option to export selectively.
  • It’s difficult to troubleshoot, if any issues arise during export.
  • Too much loose ends.

An Alternative Solution

So, is there an alternative to avoid these problems? The alternative is a small but very powerful application called Stellar Converter for EDB. With this sofwtare, you can easily open the live or a copy of the Public Folder (EDB) Exchange Database file and browse through it with no issues.

You can also search and view the items. You can export all or selective data to PST files. The application can easily handle large PST files. You can also export the data to other file formats such as EML, MSG, etc.

You can also use Stellar Converter for EDB as a migration tool. Instead of exporting to PST and then importing into Office 365, you can directly export the Public Folder to your Office 365 tenant without any limitation of PST file size or public folder size. It is the ideal migration application to shorten the migration process, without complex configurations or manual scripting.