How to Fix Error “TooManyLargeItemsPermanentException”?

In hybrid deployment, when moving mailboxes from on-premises Exchange Server to Exchange Online (Microsoft 365), you can use the migration batches. This approach helps you to migrate existing mailboxes without the need to create new user mailboxes. To start a migration batch job to synchronize data from the local Exchange Server to Exchange Online on Microsoft 365, you can use the following:

• Migration Batch Wizard in the Exchange Admin Center (Microsoft 365)
• E-Mail Migration Wizard in the Exchange Admin Center (Microsoft 365)
• Exchange Online PowerShell scripting

However, sometimes, the migration stalls or fails. When checking the log, you may notice the following error:

FailureType : TooManyLargeItemsPermanentException
FailureSide : Target
Message : Error: This mailbox exceeded the maximum number of large items that were specified for this request. --> MapiExceptionMaxSubmissionExceeded: IExchangeFastTransferEx.TransferBuffer failed (hr=0x80004005, ec=1242)

In the error message above, you can see that the target system, i.e., Exchange Online, is complaining that one of the mailboxes in the migration job has exceeded the migration limit (150 MB) of a particular item or items. Thus, stopping the process and interrupting the migration.

Solutions to Fix “TooManyLargeItemsPermanentException” Error

To fix the issue, you need to first find the affected mailbox or mailboxes and then remove the large items from the user’s mailbox on the on-premises server. After that, you need to manually restart the migration batch. You can use Outlook, EAC, or PowerShell cmdlets to find the mailbox and remove the items.

Use Outlook

You can use the Outlook options to see the size of the mailbox folders. Then, you can remove or move the large items to PST file. Here are the steps:

• Open Outlook.  
• Open the Inbox folder.
• Click on By Date.
• Make sure that All Mail is selected.
• Click on Size.

This will list the items from largest to smallest. You can then remove the large items or export them to a local PST file.

After this, you can open the Exchange Admin Center on the local server and resume the migration batch.

Use the Exchange Admin Center (EAC)

Using the Exchange Admin Center (EAC), you can import a PST file into a mailbox if you have the Mailbox Import Export role assigned. Follow these steps:

• Click on Recipients and then click on the target mailbox.
• Click on the three dots and click on Import PST.

• Type in the UNC path of the PST file.

• Select the target mailbox and confirm it.

• Select if you wish to receive a notification when this is completed.

• Click Finish.

You will still get the same error if the limit is set on the target mailbox.

Use the PowerShell Cmdlets

You can also use the PowerShell cmdlets to identify large items in a mailbox.

After opening the Exchange Management Shell (EMS), run the Get-MailboxFolderStatistics command as given below.

Get-Mailbox -ResultSize Unlimited | Get-MailboxFolderStatistics -IncludeAnalysis -FolderScope All | Where-Object {(($_.TopSubjectSize -Match "MB") -and ($_.TopSubjectSize -GE 150.0)) -or ($_.TopSubjectSize -Match "GB")} | Select-Object Identity, TopSubject, TopSubjectSize | Export-CSV -path "C:\morethan150.csv" -notype

This command will give a report of all the mailboxes with the subject of the email, along with the size of all emails that exceed the 150 MB threshold. From this report, you can easily find the large items.

Now, you can use a third-party application, called MFCMAPI, to see the mailboxes of the users and extract or remove the conflicting items.

The Best Solution

As you can see, the above methods will consume a lot of time and resources to get the results. You need to go through each and every mailbox and delete the conflicting items. To avoid such hassles and save time, you can use EDB to PST Converter, such as Stellar Converter for EDB. With this application, you can easily open the EDB files, browse through them, and granularly export the data to PST and other file formats. You can also export the EDB data directly to a live Exchange Server database or an Microsoft 365 tenant with no size limit. The application offers features such as parallel exports, priority exports, automatic mailbox matching, and continuation in case of interruption. You can export/migrate user mailboxes, archives, shared mailboxes, disabled mailboxes, and public folders with ease and in less time and resources.