Office 365 Migration Issues

Please find a list of migration issues and resolutions that I captured during my last customers migration:-

Flood mitigation on Threat Management Gateway (TMG) -



Issue Resolution
The operation couldn't be performed because object couldn't be found on '' The object has not been replicated to Office 365, check Dirsync error logs, dirsync email errors. Ensure these errors have all been resolved before the users are added to migration list and ensure the object has been sync’d to O365

A large item was encountered: Item (IPM.Note) Subject:"4600562666", Size: 42.07 MB (44,113,161 bytes), Folder:"Inbox

A large item was encountered: Item (IPM.Note) Subject:"Here's My Card", Size: 42.43 MB (44,493,004 bytes), Folder:"Inbox"

A large item was encountered: Item (IPM.Note) Subject:"", Size: 48.49 MB (50,848,177 bytes), Folder:"PRIVATE EMAILS"


ExMerge -

Search-Mailbox – Needs to be a 2010 mailbox

To be able to use the -DeleteContent Parameter you need to have "Mailbox Import Export" permissions. Without these permissions, the parameter -DeleteContent is not available for the Search-Mailbox Command.


1. Create a new Security Group

2. Enter the following command in Exchange Management Shell (replace the Security Group name accordingly):

Domain is not an accepted domain for your organization Remove all SMTP addresses from mailboxes that are not registered in O365 (or register the domain names)
Target user already has a primary mailbox. Mailbox already migrated User has already been migrated, ensue no users are duplicated
The target mail user doesn't have an SMTP address that matches the target delivery domain '' Add the target domain SMTP ( to all mailboxes before migration (and ensure they have been sync’d to O365)

Warning: Failed to clean up the source mailbox after the move.

Error details: MapiExceptionNotFound: Unable to delete mailbox. (hr=0x8004010f, ec=-2147221233)

The issue occurs when migrated accounts cannot clear homemdb, homemta, msexchhomeservername and msexchguid attributes from the source server and set the TargetAddress on the source side which it is supposed to do after mailbox move completes (flipping of the attributes starts after 95% completion of the move). A script can be created or apply this hotfix -

Pretty much the same issue as large item count

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

Pretty much the same issue as large item count

Written by Daniel Kenyon-Smith

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