Office 365 Migration Issues — Fixes for the 11 Most Common Failures (2026)
We get two kinds of migration calls: "please migrate us" and — more often than you'd think — "our migration is stuck and people can't work." This post is the field guide for the second call. Every issue below is something we have fixed in production, usually at an inconvenient hour.
Batch and sync failures
1. Migration batch stuck on "Syncing" for days
Causes, in order of likelihood: source-side throttling (EWS limits on hosted Exchange, Google export quotas), oversized items hitting transfer limits, or a batch that quietly hit a corrupt item and stopped advancing.
Get-MigrationUser -BatchId <batch> | Get-MigrationUserStatistics — look at SyncedItemCount vs TotalItemCount over an hour. Rising = throttled, be patient or raise source limits. Frozen = restart that user's move: Remove-MigrationUser, re-add in a fresh batch.2. Migration status "NeedsApproval"
Not an error — the batch was created with manual completion, or skipped items exceed the approval threshold and Exchange wants a human to accept the data loss before completing.
Get-MigrationUserStatistics -Identity user@domain | Select -Expand SkippedItems), then approve: Set-MigrationBatch <batch> -ApproveSkippedItems and Complete-MigrationBatch <batch>. If the skipped items matter (calendar items often do), export them from source first.3. "Bad item limit exceeded" / TooManyBadItemsPermanentException
Corrupt or unreadable items in the source mailbox exceeded the batch's tolerance.
Set-MoveRequest user@domain -BadItemLimit 100 -AcceptLargeDataLoss. Then verify what was actually skipped — 90% of the time it's ancient calendar corruption nobody will miss; 10% it's the CFO's contacts.4. TransientFailureSource / repeated transient errors
The source server is dropping connections — undersized on-prem Exchange, EWS throttling policy, or a proxy/firewall timing out long-running requests.
Get-ThrottlingPolicy), raise EwsMaxConcurrency for the migration account, and exclude migration traffic from SSL inspection on the firewall. Hosted source you don't control: shrink batch sizes and let delta sync grind it out.5. "Mailbox size exceeds target quota"
Source mailbox is bigger than the target's 50 GB (Business/E1) or 100 GB (E3/E5) primary quota.
Post-cutover user pain
6. Outlook keeps asking for password after migration
The #1 Monday-morning ticket. Outlook is still trying legacy auth against the old server, or the Windows Credential Manager holds stale credentials, or the profile predates Modern Auth.
Get-OrganizationConfig | fl OAuth*) → if the profile still points at on-prem, create a fresh Outlook profile. Fleet-wide prompts = check that Autodiscover DNS actually cut over (next issue).7. Autodiscover not working after migration
Clients still resolve Autodiscover to the decommissioned/on-prem server. Classic causes: internal DNS zone still hosts an old autodiscover A record, the on-prem SCP in Active Directory still points at dead Exchange, or the CNAME to autodiscover.outlook.com was never created.
autodiscover.yourdomain.com CNAME autodiscover.outlook.com. Internal DNS: kill any A/CNAME overrides. Domain-joined fleet: remove the stale SCP — Get-ClientAccessService | Set-ClientAccessService -AutoDiscoverServiceInternalUri $null on the old server, or strip it via ADSI Edit after decommission. Test with Test-OutlookConnectivity / testconnectivity.microsoft.com.8. Outlook rules not working after migration
Client-side rules reference old-environment object IDs; rules pointing at moved folders break silently.
/cleanrules switch (nukes all rules — export first).9. Outlook search not working / notes missing after migration
Search: the local index is rebuilding against a new OST — can take hours; incomplete results meanwhile are normal. Notes: they migrated, but the Notes module is hidden or they landed in a different folder tree.
Planning-stage traps
10. Migration endpoint creation fails
New-MigrationEndpoint errors usually mean the migration admin account lacks impersonation rights, EWS is blocked at the firewall, or Basic auth assumptions on a Modern-auth-only source.
ApplicationImpersonation to the migration account on the source, confirm https://source/EWS/Exchange.asmx is reachable from the internet, and use the right endpoint type (Outlook Anywhere for legacy, MRS proxy for hybrid: enable via Set-WebServicesVirtualDirectory -MRSProxyEnabled $true).11. Throttling limits killing throughput
Microsoft ingest throttling (Mailbox Replication Service) plus source-side limits mean big-bang weekends fail on math alone: 500 mailboxes × 8 GB does not fit through one weekend window.
Our Microsoft-certified team delivers seamless migrations with zero downtime.
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Sreenivasa Reddy G
Founder & CEO • 15+ years
Sreenivasa Reddy is the Founder and CEO of Medha Cloud, recognized as "Startup of the Year 2024" by The CEO Magazine. With over 15 years of experience in cloud infrastructure and IT services, he leads the company's vision to deliver enterprise-grade cloud solutions to businesses worldwide.
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