How to Migrate Mailboxes from Exchange to Office 365. Migrating mailboxes from Exchange to Office 365 is a complex process. Especially for organizations with large amounts of data and multiple mailboxes. However, with a proper planning and execution, we migrate seamlessly without disrupting day to day operations.
This article explains with step by step guide on migrating mailboxes from Exchange to Office 365. We cover everything from pre-migration planning and preparation to the migration process and post migration tasks. By following these steps, organizations successfully transition to Office 365 and take advantage of its powerful collaboration and productivity features.
Ultimate Exchange to Office 365 Migration Guide in 2025
Importance of Microsft Office 365 Migration
Companies may consider hosting their Exchange services on premises for a variety of reasons. The capacity to manage all hardware and data is one of the most crucial aspects, offering full access for troubleshooting if necessary. However, this process comes at the cost of more extraordinary maintenance expenses and 100% availability.
When we switch from on premise to Office365, we get several essential benefits. Some of them consist of the following:
- Office 365 provides all the necessary tools for work, with scalability and no additional spending.
- Purchase includes hosting and email accounts, saving time and installation costs.
- It only costs once instead of an on-premise server’s expensive running costs and ongoing maintenance.
- Microsoft ensures the security of data with its disaster recovery plans.
- In case of an issue, access and control over data are maintained in Settings.
We feel assured knowing that our server is secure and up to date, if we use an automatic update service with no downtime or other such situations.
Migrate Exchange to Office 365
Migrate Exchange to Office 365 such organization’s email, calendar, and contacts data to the cloud based Office 365 is known as migration. Based on our organization’s current Exchange Server, the number of mailboxes we need to migrate. Whether we want to manage some mailboxes on-premises or migrate them fully online, Microsoft offers 3 migration types. Review and select the best choice for your Exchange migration below.
Step 1: Assess Your Current Exchange Environment
Before migrating any mailboxes to Microsoft 365 (formerly Office 365), it’s essential to assess and understand your current on-premises Exchange infrastructure. This step ensures a smooth transition and avoids unexpected compatibility issues, user disruption, or service downtime.
Why This Matters?
Failing to properly assess your environment can lead to:
Migration failure due to unsupported configurations
Misaligned licensing plans in Microsoft 365
Incomplete mailbox moves
Delays caused by DNS, networking, or throttling issues
This step also aligns with:
CIS Microsoft 365 Foundations Benchmark v1.5: Control 1.1 – “Ensure security and configuration management planning is conducted prior to migration.”
NIST SP 800-53 Rev 5: CM-2 – “Baseline Configuration”
What You Should Assess
1. Current Exchange Version Compatibility
Make sure your on-premises Exchange version supports the type of migration you plan:
| Exchange Version | Supported Migration Types |
|---|---|
| Exchange 2010 | Cutover, Staged, Hybrid |
| Exchange 2013 | Cutover, Hybrid |
| Exchange 2016 | Hybrid |
| Exchange 2019 | Hybrid |
Run this command to get your current version:
Get-ExchangeServer | Select Name, Edition, AdminDisplayVersion
2. Mailbox Count and Sizes
Analyze how many mailboxes are to be migrated and their sizes to estimate timeline and bandwidth.
Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics | Select DisplayName, TotalItemSize, ItemCount
3. Autodiscover and Outlook Anywhere Configuration
Ensure both services are correctly configured and reachable externally.
Test Outlook Anywhere:
Test-OutlookConnectivity -Protocol HTTP -RunFromServerId <YourServer> -TargetEmailAddress <test-user@domain.com>
4. Networking and Firewall Rules
Ensure ports 443 (HTTPS) and 80 (HTTP) are open.
Validate access to
outlook.office365.com,autodiscover.outlook.com, and Exchange Web Services (EWS).
5. SMTP and MX Record Configuration
You’ll eventually change your MX records to point to Microsoft 365, but you should verify where they’re currently pointing using:
nslookup -q=mx yourdomain.com
Exchange Migration Preparation Tools
Microsoft Remote Connectivity Analyzer – to test Autodiscover and Outlook Anywhere
Exchange Deployment Assistant – to generate a tailored migration plan
Step 2: Choose the Migration Method (Cutover, Staged, or Hybrid)
Choosing the right migration strategy is critical to ensuring a successful and efficient mailbox transition from your on-premises Exchange environment to Microsoft 365. Each method has different use cases, technical requirements, and business implications.
Why This Step Is Important
Selecting the wrong migration method can:
Cause delays due to unsupported Exchange versions
Create user confusion or mail flow issues
Lead to unnecessary costs or licensing changes
This step helps satisfy:
CIS Microsoft 365 Foundations Benchmark v1.5: Control 1.2 – “Establish a secure and managed onboarding strategy for cloud applications and services.”
NIST SP 800-53 Rev 5: SA-8 – “Security and Privacy Engineering Principles”
Overview of Microsoft 365 Mailbox Migration Methods
| Method | Best For | Exchange Versions Supported | User Limit | Downtime |
|---|---|---|---|---|
| Cutover | Small orgs (<150 users) | 2010, 2013, 2016 | Up to 150 | Short window |
| Staged | Medium orgs (150–2,000 users) | 2003, 2007 (hybrid not possible) | Up to 2,000 | Some |
| Hybrid | Large orgs / co-existence | 2010, 2013, 2016, 2019 | Unlimited | None |
1. Cutover Migration
What is it?
Migrates all mailboxes and Exchange components in a single batch to Microsoft 365. Best for small organizations.
Requirements:
Exchange 2010+ (does not support Exchange 2003/2007)
Single forest, single domain
Pros:
Simple setup
Fast migration (few days)
Cons:
No coexistence between on-prem and cloud
Requires DNS record switch at time of cutover
2. Staged Migration
What is it?
Moves mailboxes in batches over time. Best for organizations still on Exchange 2003 or 2007 or that need more flexibility during the migration.
Requirements:
Exchange 2003 or 2007
Directory synchronization set up via Azure AD Connect
Pros:
Transition over multiple days or weeks
Less user disruption
Cons:
Requires DirSync (Azure AD Connect)
Not supported for Exchange 2010 and above
3. Hybrid Migration
What is it?
Provides seamless coexistence between your on-prem Exchange and Microsoft 365. Allows you to gradually migrate mailboxes.
Requirements:
Exchange 2010 or newer
Azure AD Connect
Hybrid Configuration Wizard
Pros:
No disruption to end users
Enables single sign-on (SSO)
Unified GAL (Global Address List)
Cons:
Requires certificate-based secure mail flow
More complex configuration
How to decide which Exchange to Office 365 Migration Method to Use?
| Question | Recommended Option |
|---|---|
| Do you have fewer than 150 users? | Cutover |
| Are you using Exchange 2003/2007? | Staged |
| Do you want mailbox coexistence or plan to keep hybrid for long term? | Hybrid |
Step 3: Prepare Exchange Migration (DNS, Licensing, Security & More)
Before initiating any mailbox migration, it’s critical to prepare your Microsoft 365 and Exchange environments to ensure a secure and seamless process. This includes DNS readiness, licensing, authentication setup, and verifying permissions. Skipping this step is one of the most common causes of migration failures.
Why This Step Is Important
Improper preparation may result in:
Failed mailbox moves
Broken Autodiscover or Outlook connectivity
Login or authentication errors
Delays due to missing licenses or permissions
This step supports:
CIS Microsoft 365 Foundations Benchmark v1.5:
Control 1.3 – “Ensure a baseline configuration is defined for cloud resources.”
Control 1.5 – “Ensure secure DNS and identity services are configured.”
NIST SP 800-53 Rev 5:
AC-2(5) – “Privileged account access review before deployment”
SC-12 – “Cryptographic Key Establishment”
1. Validate Domain in Microsoft 365
Before migration, your on-prem domain (e.g., yourdomain.com) must be verified in Microsoft 365 Admin Center.
🔹 Go to: admin.microsoft.com → Settings → Domains
🔹 Add your domain and verify it using the TXT record provided.
PowerShell Command to check domains:
Connect-MgGraph -Scopes "Directory.Read.All"
Get-MgDomain
2. Configure Autodiscover and DNS Records
Ensure that your Autodiscover DNS record is correctly pointing to your on-prem Exchange (for hybrid) or Microsoft 365 (after migration).
Required DNS Records for Office 365:
| Record Type | Host | Points to | Purpose |
|---|---|---|---|
| TXT | @ | MS=xxxxxxx | Domain verification |
| MX | @ | domain-com.mail.protection.outlook.com | Mail flow |
| CNAME | autodiscover | autodiscover.outlook.com | Autodiscover |
| CNAME | sip | sipdir.online.lync.com | Skype/Teams login |
| SRV | _sip._tls | sipdir.online.lync.com | Skype/Teams service |
Check your current DNS:
nslookup -type=mx yourdomain.com
3. Assign Office 365 Licenses
Each mailbox to be migrated requires a valid Office 365 license with Exchange Online included (e.g., Business Standard, E3, or E5). Licenses must be assigned before mailbox migration, Why ?
Exchange Online Mailbox Creation:
Microsoft 365 will only create a cloud mailbox after a license with Exchange Online is assigned. Without this license:Migration batch will fail
No target mailbox exists to receive migrated data
Directory Sync Dependencies (for Staged/Hybrid):
If using Azure AD Connect (Hybrid or Staged migrations), synced users appear in Microsoft 365 but won’t have mailboxes until a license is applied.
What Happens If You Don’t Assign a License?
- The migration batch throws an error:
A cloud mailbox does not exist for user@domain.com. Assign a license before proceeding.
- For staged/hybrid migrations, mailbox provisioning will not complete until licensing is resolved.
Best Practice Workflow
| Step | Action |
|---|---|
| 1 | Sync users to Microsoft 365 (if applicable) |
| 2 | Assign license with Exchange Online to each target user |
| 3 | Wait a few minutes (~15–30 mins) for the mailbox to provision |
| 4 | Start mailbox migration |
PowerShell Example to assign a license:
Connect-MgGraph -Scopes "User.ReadWrite.All"
Set-MgUserLicense -UserId user@domain.com -AddLicenses @{SkuId='ENTERPRISEPACK'}
Check unlicensed users:
Get-MgUser -Filter "AssignedLicenses eq null"
4. Set Up Authentication (MFA, SSO, Conditional Access)
Prepare users for identity changes by enabling secure authentication methods:
MFA (Multi-Factor Authentication): Enforce for all users and admins
SSO (Optional): If using hybrid identity via Azure AD Connect
Conditional Access Policies: Block legacy protocols, restrict logins by country/IP
CIS Benchmark Control Mappings:
Control 2.3.1 – “Ensure Modern Authentication is enabled”
Control 2.6.1 – “Ensure MFA is enabled for all users”
PowerShell (Graph SDK) to check MFA state:
Get-MgUserAuthenticationMethod -UserId user@domain.com
5. Grant Mailbox Permissions and Test Access
Ensure the admin account running the migration has:
ApplicationImpersonation role
FullAccess permissions (for hybrid/staged)
PowerShell to assign impersonation:
New-ManagementRoleAssignment -Role "ApplicationImpersonation" -User MigrationAdmin
Test Mailbox Access:
Test-Mailbox -Identity "user@domain.com"
6. Directory Sync (Hybrid or Staged Only)
Install and configure Azure AD Connect to sync your on-prem AD users with Microsoft 365.
Download from: https://aka.ms/aadconnect
Use password hash sync for most migrations
Optional: Enable Seamless SSO
Verify Sync Status:
Get-MsolUser -Synchronized
7. Plan for Downtime and User Communication
Prepare for:
Possible short downtime during cutover
Informing users of new login procedures
Setting up redirection for Outlook profiles
Create a communication plan that includes:
Migration date and expected downtime
Login instructions post-migration
FAQs and support contact
Step 4: Execute the Migration (Cutover, Staged, Hybrid)
Now that you’ve assessed your environment and completed pre-migration tasks, it’s time to begin migrating mailboxes. This step walks you through how to execute a mailbox migration using Cutover, Staged, or Hybrid methods — via both the Microsoft 365 GUI and PowerShell commands.
Why This Step Is Critical
Improperly executing your migration can result in:
Incomplete or failed mailbox moves
Email downtime or mail loss
Broken Outlook profiles
Missed compliance expectations
This step supports:
CIS Microsoft 365 Foundations Benchmark v1.5:
Control 1.6 – “Ensure secure transition to cloud services with validated testing.”
NIST SP 800-53 Rev 5:
SI-2(6) – “System and Communications Protection – Migration Testing and Validation”
A) Execute a Cutover Migration
Best for: Small organizations with <150 mailboxes
Supported Exchange Versions: Exchange 2010, 2013, 2016
Unsupported: Exchange 2003, 2007, or hybrid deployments
Tools Required: Exchange Admin Center (EAC), Microsoft 365, Outlook
A cutover migration transfers all mailboxes to Office 365 at once. Additionally, small businesses with email systems that use the Exchange admin center (EAC) use this “migrate to office365” technique.
Since the process moves quickly and simultaneously, we refer to these frequent Exchange migrations as “cutovers.” Ideal for handling enormous mailboxes, such as those found in large enterprises or government organizations that must complete things quickly before deadlines approach.
1. Verify prerequisites:
Domain is verified in Microsoft 365
Autodiscover is working externally
Admin account has full access to all mailboxes
2. Prepare Exchange for Migration:
Ensure all mailboxes are visible to the admin account
Disable Unified Messaging if enabled
3. In Microsoft 365 Admin Center:
- In the Exchange admin center, go to Migration, and select Add migration batch.
2. On the Add migration batch page,
- Give migration batch a unique name: Type a migration name, for example, HR_Migration2.
- Select the mailbox migration path: Verify that Migration to Exchange Online is selected.
3. Configure Migration Setttings:
Provide on-premises Exchange credentials
Microsoft 365 auto-discovers settings
4. Start the batch:
Choose “Automatically start” and “Automatically complete” options (recommended for cutover)
5. Wait for synchronization to complete:
Migration status can be monitored from the EAC
Expect it to take several hours, depending on mailbox size/count
6. Update DNS Records:
Once the batch completes, update your MX, Autodiscover, and SPF records to point to Microsoft 365
7. Assign licenses to each user (if not done earlier)
8. Reconfigure Outlook clients:
After DNS propagation, Outlook will auto-configure to Microsoft 365
Office 365 Cutover Migration PowerShell Steps
1. Connect to Exchange Online & Create Migration Endpoint:
$onPremCred = Get-Credential
New-MigrationEndpoint -Name "CutoverEndpoint" -ExchangeRemoteMove -RemoteServer mail.domain.com -Credentials $onPremCred
2. Start the Batch:
New-MigrationBatch -Name "CutoverBatch" -SourceEndpoint "CutoverEndpoint" -AutoStart -AutoComplete
B) Staged Migration
Best for: 150–2,000 users
Supported Exchange: 2003, 2007
Requires: Azure AD Connect, CSV of users, staged batches
Staged migration moves mailboxes from Exchange 2003 or 2007 to Microsoft 365 in multiple batches over time. It’s ideal for organizations that want to move in phases, not all at once (like in a cutover migration). To prevent downtime, it’s crucial to arrange the users’ mailbox migration from one platform (i.e., source) to another while migrating from Exchange to Office 365. For instance, if we use Microsoft 365 or Office 365, we migrate data in stages rather than all at once, which could take hours, if done correctly.
Staged Migration Prerequisites
Verify your domain in Microsoft 365
Prepare your on-prem Exchange environment:
Set mailbox UPNs to match the user’s primary email address
Assign FullAccess to the admin account
Configure Azure AD Connect and synchronize users to Microsoft 365
Assign Microsoft 365 licenses to synced users
Ensure mail-enabled users exist in Microsoft 365 before migration
1. Prepare Migration CSV
First step is to prepare a CSV file containing users details. The CSV file for a staged migration supports the following three attributes. Each row in the CSV file corresponds to a mailbox and must contain a value for each of these attributes.
| Attribute | Description | Required? |
|---|---|---|
| EmailAddress | Specifies the primary SMTP email address, for example, pilarp@contoso.com, for on-premises mailboxes. Use the primary SMTP address for on-premises mailboxes and not user IDs from the Microsoft 365 or Office 365. For example, if the on-premises domain is named contoso.com but the Microsoft 365 or Office 365 email domain is named service.contoso.com, you would use the contoso.com domain name for email addresses in the CSV file. | Required |
| Password | The password to be set for the new Microsoft 365 or Office 365 mailbox. Any password restrictions that are applied to your Microsoft 365 or Office 365 organization also apply to the passwords included in the CSV file. | Optional |
| ForceChangePassword | Specifies whether a user must change the password the first time they sign in to their new Microsoft 365 or Office 365 mailbox. Use True or False for the value of this parameter. If you implemented a single sign-on solution by deploying Active Directory Federation Services (AD FS) 2.0 (AD FS 2.0) or greater in your on-premises organization, you must use False for the value of the ForceChangePassword attribute. | Optional |
Here’s an example of the format for the CSV file. In this example, three on-premises mailboxes are migrated to Microsoft 365 or Office 365.
The first row, or header row, of the CSV file lists the names of the attributes, or fields, specified in the rows that follow. Each attribute name is separated by a comma.
EmailAddress,Password,ForceChangePassword
mikep@infrasos.com,Pa$$w0rd,False
terryn@infrasos.com,Pa$$w0rd,False
sallyt@infrasos.com,Pa$$w0rd,False
Exchange Admin Center Migration Steps
In the new Exchange Admin center, navigate to Migration > Batch.
Select New Migration batch and follow the instructions in the details pane.
In Migration Onboarding section, enter the batch name, select the mailbox migration path and select Next.
Select the migration type as Staged migration from the drop-down list and select Next.
5. In Prerequisites section, read the following and select Next.
6. In Set endpoint section, you can either create a new migration endpoint or select the migration endpoint from the drop-down list: a. Select Create a new migration endpoint and follow the instructions to create the endpoints. b. Select the migration endpoint from the drop-down list and select Next.
7. Select and upload a CSV file containing the set of all of the users you want to migrate. The allowed headers are:
EmailAddress (required). Contains the primary email address for an existing Microsoft 365 or Office 365 mailbox.
Username (optional). Contains the Gmail primary email address, if it differs from EmailAddress.
8. In Add user mailboxes section, import the CSV file and select Next.
9. In Move configuration section, enter the details and select Next.
10. In Schedule batch migration section, verify all the details, select Save, and then select Done.
The batch status changes from Syncing to Synced, you can complete the batch.
11. To complete the batch, select the migration group.
12 In the details pane, select the preferred option to complete the batch and select Save.
The batch status is then Completed.
PowerShell Steps (Optional)
- Connect to Exchange Online and create a migration endpoint:
$onPremCred = Get-Credential
New-MigrationEndpoint -Name "StagedEndpoint" -ExchangeRemoteMove -RemoteServer mail.yourdomain.com -Credentials $onPremCred
2. Create and start the batch:
New-MigrationBatch -Name "StagedBatch01" `
-CSVData ([System.IO.File]::ReadAllBytes("C:\StagedUsers.csv")) `
-SourceEndpoint "StagedEndpoint" `
-AutoStart:$true `
-AutoComplete:$false
3. Manually complete after verifying success:
Complete-MigrationBatch -Identity "StagedBatch01"
Post-Batch Actions
Assign Microsoft 365 licenses to newly synced users
Update MX records to point to Microsoft 365
Reconfigure Outlook profiles
Remove batch if complete:
Remove-MigrationBatch -Identity "StagedBatch01"
C) Hybrid Migration
Hybrid migration enables full coexistence between on-premises Exchange and Microsoft 365. It allows mailboxes to be moved in small batches, while maintaining a shared GAL (Global Address List), calendar free/busy info, and centralized mail flow.
Best Use Case
| Scenario | Supported |
|---|---|
| Long-term coexistence | ✅ |
| Gradual mailbox moves | ✅ |
| >2,000 users | ✅ |
| Exchange 2010/2013/2016/2019 | ✅ |
| Exchange 2007 or earlier | ❌ |
Prerequisites
Exchange Server: Exchange 2010 SP3 or later
Azure AD Connect: Configured for directory sync
Hybrid License: You can request a free Exchange Hybrid license
Publicly trusted SSL certificate (e.g. for mail.domain.com)
Public Autodiscover and EWS URLs must resolve externally
Admin credentials for both Microsoft 365 and Exchange
Key Components
Hybrid Configuration Wizard (HCW): A tool that configures all connectivity
OAuth Authentication: Required for secure cloud <-> on-prem comms
Migration Endpoint: Used to create move requests
Mail Flow Connector: Optional for centralized routing
GUI Steps (Official Hybrid Migration)
1. Run Hybrid Configuration Wizard
👉 Download here: https://techcommunity.microsoft.com/blog/exchange/updated-hybrid-configuration-wizard-available/3859905
Run HCW on Exchange 2016/2019 server (or dedicated hybrid server)
Sign in to both your on-prem Exchange and Microsoft 365 tenant
Choose the type of hybrid:
Minimal Hybrid (good for short-term moves only)
Full Hybrid (recommended for full coexistence)
2. Validate HCW Completion
It configures:
Mail flow connectors (inbound & outbound)
Federation trust and organization relationship
Autodiscover redirection
Migration endpoint in Microsoft 365
PowerShell Steps (Mailbox Migration Only)
Once HCW is completed, you can move mailboxes using Exchange Online PowerShell:
# Connect to Exchange Online
Connect-ExchangeOnline
# Initiate a move request for a user
New-MoveRequest -Identity user@domain.com
To view status:
Get-MoveRequest | Get-MoveRequestStatistics
To remove completed requests:
Get-MoveRequest | Remove-MoveRequest
Mail Flow Options in Hybrid
| Option | Description |
|---|---|
| Centralized Mail Transport | Mail flows from Exchange Online → on-prem for outbound |
| Decentralized Mail Flow | Mail is delivered directly from Microsoft 365 |
Choose during HCW setup. Most organizations do NOT need centralized mail flow unless specific compliance policies require it.
Gotchas & Best Practices
| Concern | Best Practice |
|---|---|
| Certificates | Must match public DNS name (mail.domain.com) |
| Licensing | Assign Microsoft 365 Exchange Online license before mailbox move |
| DNS | Leave Autodiscover pointing to on-prem until final cutover |
| Outlook | Autoconfigures automatically post-migration |
Hybrid Office 365 Migration Checklist
Domain Verified in Microsoft 365
Azure AD Connect Sync Working
SSL Certificate Installed
External EWS/Autodiscover Test Passed
HCW Completed Without Errors
Migration endpoint verified
Mail flow tested post-move
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Step 5: Post-Exchange to M365 Migration Tasks and Cleanup
After mailboxes have been successfully migrated to Microsoft 365 using Cutover, Staged, or Hybrid migration, your job isn’t quite finished. This step ensures smooth end-user experience, maintains security posture, and removes legacy configurations no longer needed.
Why This Step Matters
Neglecting post-migration tasks can lead to:
Mail flow issues due to DNS misconfiguration
Outlook connectivity problems
Confusion around legacy server roles
Security misalignment with compliance standards
Compliance Mapping
| Framework | Control | Description |
|---|---|---|
| CIS Microsoft 365 v1.5 | 3.5 – Secure DNS Settings | Ensure MX and Autodiscover records point to Microsoft 365 |
| NIST 800-53 Rev 5 | SC-12 – Cryptographic Key Establishment | Applies to TLS and secure mail flow verification |
| ISO/IEC 27001 | A.13.2.1 – Information transfer policies and procedures | Ensures secure transition and mail routing after migration |
Tasks by Migration Type
| Task | Cutover | Staged | Hybrid |
|---|---|---|---|
| Assign Licenses | ✅ Before move | ✅ Before move | ✅ Before move |
| DNS Update (MX, SPF, Autodiscover) | ✅ | ✅ | 🕒 Final step |
| Remove Migration Batch | ✅ | ✅ | N/A (manual move reqs) |
| Decommission On-Prem Servers | ✅ Optional | ✅ Optional | ❌ (keep at least 1 Exchange server) |
| Test Mail Flow | ✅ | ✅ | ✅ |
| Remove Legacy Mailboxes | ✅ | ✅ | ✅ |
Step-by-Step Post-Migration Tasks
1. Complete and Remove Migration Batch
For Cutover & Staged migrations:
# Complete batch if not auto-completed
Complete-MigrationBatch -Identity "CutoverBatch"
# Remove the completed batch
Remove-MigrationBatch -Identity "CutoverBatch"
For Hybrid:
# Remove completed move requests
Get-MoveRequest | Remove-MoveRequest
2. Update DNS Records
Ensure all DNS entries now point to Microsoft 365:
| Record | Points To |
|---|---|
| MX | domain-com.mail.protection.outlook.com |
| SPF | v=spf1 include:spf.protection.outlook.com -all |
| Autodiscover | autodiscover.outlook.com |
| CNAMEs | sip, lyncdiscover, msoid, etc. |
Use this tool to verify: https://mxtoolbox.com/
3. Test Mail Flow & Outlook Autoconfig
Use the Microsoft Remote Connectivity Analyzer:
🔗 https://testconnectivity.microsoft.com
Verify:
External mail arrives to Microsoft 365 inbox
Internal Outlook clients auto-configure via Autodiscover
SPF, DKIM, and DMARC are functioning properly
4. Clean Up On-Prem Exchange (Optional)
Applies to Cutover and Staged migrations only.
If you’re fully decommissioning on-prem Exchange:
Migrate any remaining Public Folders
Remove mailboxes from local AD (after sync disabled)
Uninstall Exchange:
Setup.exe /Mode:Uninstall /IAcceptExchangeServerLicenseTerms
💡 For Hybrid, you must keep at least 1 Exchange server for managing recipients (or use 3rd party tools).
5. Monitor Microsoft 365 Post-Migration
Enable reporting for compliance & health:
# Example: View mailbox sizes
Get-Mailbox | Get-MailboxStatistics | Sort TotalItemSize -Descending | Select DisplayName, TotalItemSize
# Example: Audit recent logins
Search-UnifiedAuditLog -StartDate (Get-Date).AddDays(-7) -EndDate (Get-Date) -Operations UserLoggedIn
Also use:
- InfraSOS Office 365 Reporting & Auditing
Microsoft 365 Defender Portal
Microsoft Purview Compliance Portal
Secure Score Dashboard
- Office 365 Security Best Practices (Meet CIS & NIST Compliance)
6. Communicate with Users
Notify users their migration is complete
Share updated instructions for:
Outlook setup (if profile reset is needed)
Mobile devices
Webmail URL:
https://outlook.office365.com
Final Checkpoint
✅ Mail flow verified
✅ Outlook clients working
✅ DNS records updated
✅ Batches cleaned up
✅ Compliance audit trail preserved
FAQs About Migrating Exchange to Office 365
Q: Why should I migrate my mailboxes from Exchange to Office 365?
A: Office 365 provides various benefits, such as improved collaboration, access to cloud based applications, and simplified management of user accounts. Additionally, Office 365 offers better integration with other Microsoft products and services.
Q: Can I migrate all of my mailboxes at once?
A: It depends on the size of our organization and the number of mailboxes we have. We recommend migrating a few mailboxes at a time to avoid overwhelming our system and to ensure a smooth migration process.
Q: What should I consider before migrating my mailboxes?
A: Consider things like the size and complexity of our business, the volume of data we have, the compatibility of our present systems with Office 365, and the resources available for the migration process before converting our mailboxes.
Q: What are some common challenges I may face during migration?
A: Some common challenges include data loss or corruption, compatibility issues, connectivity problems, and user resistance to change.
Q: What is the estimated time for the mailbox migration process?
A: Depending on our organization’s size and complexity, the volume of data we have, and the resources available for the conversion process. Generally speaking, it takes a few days to a few weeks.
Q: Do I need to back up my data before migrating to Office 365?
A: Yes, we recommend backing up our data before migrating to Office 365 to prevent corruption or data loss during the migration process.
Q: Can I use a third-party tool to migrate my mailboxes to Office 365?
A: Yes, many third-party tools help with the mailbox migration process. Essential to choose a reputable tool and ensure it’s compatible with our current system and Office 365.
Thank you for reading How to Migrate Mailboxes from Exchange to Office 365. We shall conclude this article now.
Migrate Exchange to Office 365 Conclusion
In conclusion, migrating mailboxes from Exchange to Office 365 is complex. Still, with careful planning and execution, we seamlessly do it without disrupting day-to-day operations. It’s crucial to consider aspects like our organization’s size and complexity, the volume of data we have, and the resources available for the conversion process. Additionally, to ensure we have a copy of all our data in case any is lost or corrupted during the migration process, we advise backing up our data before the migration.
By following the step-by-step guide and considering these factors, organizations successfully transition to Office 365 and take advantage of its powerful collaboration and productivity features.
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Comment (1)
charlote
May 21, 2023I use Gs Richcopy 360, it is the best for migrating to Office 365