How to Migrate Outlook to Office 365? (Emails, Calendars, etc)

To move Outlook to Office 365 means transferring all your Outlook data, emails, calendars, account settings, profiles, rules, and more.

What gets migrated depends on the type of account you use and the Outlook data file you’re moving. Different migration methods move different components, and this guide explains each one.

Why This Guide Works?

This guide is based on verified, real-world testing. Our team has successfully migrated hundreds of accounts from Outlook 2016, 2019, and 2021 to Microsoft 365.

We developed these five methods after facing and overcoming common migration failures (like oversized PSTs and lost rules/signatures) found in other online articles.

The steps and Pro Tips included here are the validated solutions that ensure a complete and reliable Outlook data transfer for every user.

Pre-Migration Checklist before Transferring Outlook to Office 365

• Verify Office 365 Licenses: Make sure all users are properly licensed before migration.
• Back Up Existing Data: Always back up your current Outlook data before moving to Office 365.
• Clean Up Mailboxes: Reducing mailbox size helps speed up and smooth the migration
• Check System Requirements: Ensure your system meets the minimum requirements for a successful migration.
• Communicate with Users: Prepare users so they know what to expect during the migration.

Best Ways to Migrate Outlook Email to Office 365

Below are all workable migration options, from beginner-friendly to advanced IT methods:

Migration Method	Best For	Key Data Migrated
PST Import/Export	Single-user data movement	Emails, Contacts, Calendar (Must manually recreate rules/signatures).
Drag-and-Drop	Quick, selective transfer of small data sets	Real-time, selective items between two visible mailboxes
Network Upload	Enterprise bulk migration (IT Admin)	Large volumes of PST data to the server via Azure
Professional Tools	Moving the entire Outlook profile	Everything (Data, Settings, Rules, Signatures, NK2).
OST Conversion	Recovering data from inaccessible local OST files	Data within the OST (Requires conversion to PST).

Method 1: Migrate Outlook to Office 365 Using Import/Export (PST File)

This method moves your emails, contacts, and calendar, but it does not migrate rules, signatures, profiles, or autocomplete data.

Step 1: Export the .pst file

• Open Outlook, Go to File > Open & Export > Import/Export.

• Select Export to a file > Outlook Data File (.pst).

• Choose your mailbox & tick include subfolders.

• Save the PST file.

Step 2: Add Your Office 365 Account

• Install Outlook on the new PC.
• Go to File > Add Account.

• Sign in using your Microsoft 365 email.

Step 3: Import the .pst File

• Go to File > Open & Export > Import/Export.
• Select Import from another program or file > .pst.

• Choose Do not import duplicates
• Import into your Office 365 mailbox

Pro Tip: For mailboxes larger than 20GB, consider splitting exports by folder or date range to create multiple smaller PST files.

Method 2: Drag-and-Drop Migration (Quick Selective Method)

This method is fast and requires no file creation, offering real-time and selective transfer for small data sets.

However, it is not suitable for large mailboxes, requires both accounts in the same Outlook profile. This can fail if connectivity drops, and it doesn’t support automation for multiple users.

Step 1: Add both accounts to Outlook

• Add your old email account (POP, IMAP, or Exchange)
• Add your Office 365 account
• Both should appear in the Folder Pane

Step 2: Drag folders or individual emails into the Office 365 mailbox.

• Select folders or individual emails from the source account
• Drag them to the corresponding folders in the Office 365 account
• Hold Ctrl while dragging to copy (vs. move)
• For bulk selection: Use Ctrl+Click or Shift+Click

Step 3: Verify the process,

• Watch the bottom status bar for sync progress
• Large folders may take several minutes
• Outlook will display “All Folders are up to date” when complete

Once the folders are transferred, check the folders and test a few emails to ensure they open correctly.

Method 3: Microsoft Network Upload

This method is best for organizations migrating multiple large mailboxes, enterprise migrations. Microsoft’s Network Upload method allows you to upload PST files directly to Microsoft’s Azure storage, then import them into Microsoft 365 mailboxes through the admin center.

Steps:

Phase 1: Prepare PST Files

• Export each mailbox to a PST file.
• Name PSTs clearly and keep them all in one folder.
• Keep PSTs under 20 GB for smoother processing.
• Create a mapping CSV that tells Microsoft which PST belongs to which mailbox

Phase 2: Network Upload to Azure

• Go to Microsoft 365 Compliance Center >Data lifecycle management > Import.
• Create a new import job and select Network upload.
• Copy the Azure SAS URL (valid for 14 days).
• Install AzCopy, then upload the PST folder using:
• AzCopy.exe /Source:”C:\PST_Files” /Dest:”[Your_SAS_URL]” /V:”C:\Logs\upload.log” /Y

Phase 3: Import PST Files to Mailboxes

• In the Compliance Center, upload your mapping CSV and validate it.
• Start the import, choose the target mailboxes, and apply optional filters.
• Outlook imports the PSTs in the background; progress is shown in the portal, and email notifications are sent when it’s done.

Method 4: Transfer Outlook to Office 365 Using Professional Migration Tools

This method is ideal if you want to move everything from your old Outlook setup without missing any data.

Remo Outlook Backup and Migrate is an effective tool that can back up your entire Outlook profile, including emails, OST/PST data, rules, and signatures.

Remo Outlook Migration tool helps import Outlook settings to a new computer, including AutoComplete (NK2), calendar, contacts, and tasks in a few easy steps.

• Launch the Remo Outlook Transfer Tool on the computer with your Outlook data.
• On the home screen, click Backup, choose a backup option, create a backup copy, and save it.

Now, copy the backup file to another computer if you wish to move Outlook to new computer for Office 365 migration.

• Close Outlook and launch Remo Outlook Migration software. Click Migrate.

• Locate the saved Outlook backup file and verify the Outlook version displayed, and click Next.

• Select the Outlook attributes you want to transfer.

• Click Finish to complete the transfer to Office 365.

Method 5: OST to Office 365 Migration

OST (Offline Storage Table) files are local cached copies of your Exchange mailbox. Unlike PST files, they are not meant for import/export and are tied to a specific Outlook profile.

Because of these limitations, OST migration becomes difficult in real-world scenarios, especially when the original server is unavailable or being decommissioned.

When moving Outlook to Office 365 or a new Exchange environment, you may have OST files containing emails that no longer exist on the server. Outlook cannot import OST files directly, so a conversion step becomes necessary.

You can choose the listed solutions below to import the OST file to Outlook:

Option A: Convert OST to PST (Recommended)

The most reliable approach is to convert the OST into a PST, which can then be imported into Microsoft 365 or Outlook.

Use a popular tool and an effective tool, Remo OST to PST converter, for converting OST files to PST, which has an easy interface, maintains the original folder structure. Especially when the OST is orphaned or Outlook won’t open

• Step 1. Download, install, and launch the Remo OST to PST Converter tool on your computer.

Step 2. Choose either Open OST File (if you want to locate the OST file manually) or Find OST File (if you want the software to locate the OST file automatically) before clicking Next.

Step 3. On the next screen, choose the Browse option to provide the destination path for the converted PST file and then click on Convert.

Step 4. The Remo OST converter tool now converts the OST file to a healthy PST file. 

Option B: Reconnect and Sync

If the old Exchange server is accessible:

• Add the old Exchange account back into Outlook
• Let Outlook sync everything with the server
• Confirm all old emails are restored
• Add your Microsoft 365 mailbox to the same profile
• Drag and drop the folders to Microsoft 365

Post-Conversion Steps: Once the OST file has been converted to PST and imported, perform cleanup by securely deleting old OST/PST files, clearing temporary export folders, and freeing up local storage.

Post-Migration: Configuring the Outlook

Once your data is successfully migrated to Office 365 (via PST Import, Drag-and-Drop, or Network Upload), you need to configure your local Outlook application to connect to the new cloud mailbox. This is a client setup step, not a data migration step.

Step 1: Prepare the Client

• Export a PST backup (optional, but safe).
• Remove the old Outlook profile via Control Panel > Mail > Show Profiles (recommended for a clean setup).

Step 2: Add Your Office 365 Account (The “Auto Account Setup”)

• Open Outlook. It launches the setup wizard automatically.
• Enter your Office 365 email address > sign in > and complete MFA.
• Outlook configures everything automatically using the Autodiscover service.
• Enable Cached Exchange Mode for faster performance.

Step 3: Let Outlook Sync and Reapply Settings

• Outlook begins downloading the content that was just migrated to your new mailbox.
• Recreate rules: File > Manage Rules & Alerts.
• Rebuild email signatures.
• Add any additional accounts if needed.

Frequently Asked Questions

About the Author: Tony Landry

Tony Landry is a Web Content Editor at Remo Software. He loves to write, edit, and manage content for users trying to troubleshoot and fix problems on Windows, Outlook, storage drives, and Cloud storage networks. With an aptitude that transcends writing, Tony is recognized as a Microsoft Outlook, Word, and PowerPoint expert. His comprehensive solutions…