There are many good reasons to move away from Microsoft 365 and migrate to an IMAP-based email provider: reducing dependency on Microsoft, cutting subscription costs, better privacy, or simply preferring a different email setup. Whatever your reasons, this tutorial explains in easy-to-follow steps how you can migrate your emails from Office 365 to IMAP.
In this article, you’ll learn what to consider before migrating, how to migrate your emails using MailJerry, how to export and import your contacts and calendars, and how to handle common errors along the way.
Summary: How to Migrate from Office 365 to IMAP
Migrating from Office 365 / Microsoft 365 to an IMAP-based email provider can be done in just a few steps. Simply connect both accounts in MailJerry, check your settings, preview your migration and click on „Start Migration“.
Practical tips for your Office 365 to IMAP migration:
- Make sure IMAP is enabled for your Microsoft 365 account before starting the migration.
- For large mailboxes (10 GB+), consider disabling EWS throttling to avoid interruptions.
- Don’t forget to export your contacts and calendars and import them to your new IMAP account separately.
💡 After the email migration, activate the auto-sync to make sure emails received in your old account are automatically forwarded to your new IMAP mailbox!
➡️ In case you still have any questions, our FAQs are here to help!
Office 365 vs. IMAPWhat’s Right For You?
Before diving into the migration, it’s worth weighing the pros and cons of each solution: Microsoft 365 is more than just email – it’s a full productivity suite. But that doesn’t mean it’s the right fit for everyone.
Reasons to Switch from Office 365 to IMAP:
- 💰 Cost savings: IMAP hosting is often significantly cheaper than a Microsoft 365 subscription, especially if you only need email and not the full Office suite.
- 👩💻 Privacy & control: With a self-hosted or independent IMAP provider, you have more control over where your data is stored and who can access it, which can make it much easier to comply with privacy protection laws like GDPR, CCPA, and HIPAA.
- 👍 Simplicity: IMAP is a universal standard. No tenant configurations, no EWS throttling – just email.
- 🧑🩰 Flexibility: IMAP works with any email client (Thunderbird, Apple Mail, Roundcube webmail, etc.) without locking you into a specific ecosystem.
- 🏋️♀️ Lighter footprint: If you don’t need Teams, SharePoint, or OneDrive, why pay for them?
Reasons to Stay with Microsoft 365
- 🌟 Integration: If you rely on Word, Excel, Teams, or OneDrive, the Microsoft ecosystem integration is hard to beat.
- 🏬 Enterprise features: Shared mailboxes, calendar delegation, and advanced security features are well-implemented. To achieve the same functionality with an IMAP-based provider, you would need to rely on third-party tools and extensions.
- 🤖 AI integration: Microsoft 365 offers built-in AI tools like Copilot that most IMAP providers can’t match.
➡️ So after weighing the pros and cons: If you’ve decided that IMAP is the way to go, let’s get started with the email migration!
Step by Step:Migrate from Office 365 to IMAP
Checklist:
What You’ll Need
Before jumping into the migration, let’s make sure you have everything at hand. This is what you need to migrate your emails from Office 365 to IMAP:
1️⃣ Your Microsoft 365 / Office 365 credentials (username + password)
2️⃣ Your IMAP credentials (username + password)
3️⃣ The address of your IMAP mail server
4️⃣ MailJerry – your Office 365 to IMAP migration tool
✅ Don’t know your IMAP server address? Have a look at our list of email settings to find the correct address. If your hosting company is not included in the list, simply ask your provider for the IMAP mail server address!
Step 01:
Set Up the Migration
Now let’s start the setup of your migration! In this step, we’ll connect your Office 365 and IMAP account so you can migrate your email data directly between your providers.
1. Download and install MailJerry or open the MailJerry WebApp.
2. Click on “New Migration”.
3. In the section “Existing Address”, select “Microsoft / Office 365” as account type.
4. Enter the username for your Microsoft account and click on “Connect with Microsoft”.
5. A Microsoft sign-in popup opens. Enter your password and click on “Sign in”.
6. Now head over to the section “New Address”. Here, select “IMAP” as account type.
7. Enter your username (usually your email address) and your password in the corresponding fields.
8. In the field “mailserver”, enter your IMAP mail server address.
➡️ For your IMAP account, MailJerry will suggest the mailserver based on your email address. If the suggestion doesn’t match your provider’s settings, enter the mailserver address as stated by your provider.
✅ You now added both accounts. In the next step, we’ll verify your settings and preview the migration.
Step 02:
Preview Your Office 365 to IMAP Migration
Now let’s check if everything is set up correctly:
9. Click on “Check Settings” and wait until the check has finished. MailJerry will connect with both accounts and gather all necessary data so you can safely preview the planned migration.
💡 If your Office 365 mailbox is very large, it might take some time to collect all necessary data. Please be patient and wait until you’re forwarded to the preview page!
10. After both mailboxes were checked successfully, you’ll see a preview of the planned migration. Here, you can verify which folders are included and how many emails will be migrated.
✅ Everything looks good? Then let’s start the migration!
Step 03:
Start the Migration from Office 365 to IMAP
Now let’s start your Office 365 to IMAP migration!
11. On the preview page, click on “Start Your Migration”. MailJerry will now migrate all messages from your Office 365 mailbox to your new IMAP account – including all folders and attachments.
✅ While the migration is running, you can use both email accounts to receive or send emails. All changes in your Office 365 account can be synced after the initial migration by running a delta migration or by enabling the auto-sync (see Step 04).
⚠️ Please avoid large structural changes in your mailbox while the migration is running (e.g. cleanup, moving lots of messages and / or restructuring folders)
"For us MailJerry is a game changer when migrating mails to MS 365, multi platform is great, the easy handling is great, everything is great.Thank you for the top of the line software!"
Step 04:After the Migration
Now that you’ve successfully migrated your emails & folders to your new IMAP account, you might wonder: What happens with emails that are still received in your old Office 365 account? For this scenario, there’s a handy feature:
1. In the MailJerry app, click on “Overview” and select your migration.
2. On the details page, scroll down to “Options”.
3. Here, click on “Automatically Synchronize Emails for 10 Days”.
✅ Now, your old account will be synced with your new account every three hours. This means that emails received in your Office 365 account will automatically be migrated to your IMAP account. You can sync your accounts at any time by clicking on the “Sync Now” button on the details page.
Do You Wish to Sync Your Data Permanently?
In this case, activate the backup mode:
1. On the details page, click on “Backup Mode”.
2. Activate the option “Permanently Sync Emails to Target Mailbox”.
3. Optionally, you can change the backup interval from monthly to weekly or daily.
✅ By activating the backup mode, your emails will permanently be synced to your IMAP mailbox, without any time limitation!
How ToMigrate Contacts from Office 365 to IMAP
Now you’ve migrated your messages and folders from Office 365 to IMAP – but your contacts are still missing. Contacts are stored separately from your mailbox data, so you’ll need to export them from Office 365 and import them into your new IMAP account manually.
How to Export Contacts from Office 365 (Outlook on the Web):
1. Log in to Outlook on the Web with your Microsoft 365 credentials.
2. At the top of the side panel, select the “People” icon to go to the contacts page.
3. On the toolbar, select “Manage contacts” > “Export contacts”.
4. Choose to export either “All contacts” or just contacts from a specific folder.
5. Click on “Export”.
✅ Your contacts are now saved as a CSV file in your computer’s Downloads folder.
How to Export Contacts from Outlook Desktop (Windows):
If you’re using Outlook Desktop on Windows, you can export your contacts via File > Open & Export > Import/Export > Export to a file > Comma Separated Values (CSV).
How to Import Contacts to Your IMAP Account
How you import your contacts depends on which email client or webmail interface you use for your IMAP account. Most webmail interfaces offer a built-in contact import feature. Here’s how to do it with Roundcube, one of the most common webmail clients:
1. Log in to your webmail (e.g. Roundcube).
2. Go to the “Address Book” / “Contacts” section.
3. Click on “Import” and select your CSV file.
4. Map the fields if necessary (e.g. “First Name” → “First Name”, “Email” → “Email”).
5. Click on “Import” to complete the process.
If you prefer using a desktop email client, most of these apps also offer contact import options (e.g. via their built-in Address Book or Contacts app). Check your email client’s documentation for specific steps.
How ToMigrate Calendars from Office 365 to IMAP
Just like contacts, calendars are stored separately from your mailbox data and won’t be migrated automatically, but can easily be exported and imported into your new account:
1. Open Outlook on the Web and go to the Calendar section.
2. Click on “Add calendar” > “Upload from file”.
3. Select the calendar you want to export and download it as an .ics file.
4. Log in to your new provider’s webmail or calendar interface.
5. Look for an option to import or upload an .ics file (often found under Settings > Calendar > Import).
6. Upload your .ics file and confirm the import.
✅ Your calendar entries will now be available in your new IMAP provider’s calendar interface.
Common Errors &How to Fix Them
EWS Throttling:
Migration Stops or Slows Down
Microsoft applies email limits (“EWS throttling”) to Office 365 and Exchange Online accounts. These limits can cause issues during large email migrations, such as disconnects or incomplete migrations. Even with throttling disabled, Microsoft still limits bandwidth, so plan enough time for large migrations.
➡️ See our guide on how to migrate large Microsoft 365 mailboxes for further information.
💡 How to fix it: If you’re migrating a large mailbox (10 GB+), consider temporarily disabling EWS throttling. Follow our tutorial on how to disable EWS throttling in Office 365.
Error:
IMAP Login Failed
If MailJerry can’t connect to your Office 365 account, IMAP might be disabled. This is a common issue and easy to fix.
💡 How to fix it: Check out this tutorial on how to enable IMAP for Office 365 / Microsoft Exchange accounts.
Problem:
Messages Larger Than 25 MB Are Rejected
When migrating from Office 365 to IMAP, it’s possible that your Microsoft 365 account contains emails with attachments larger than 25 MB (especially if you previously increased the Office 365 max message size. If your new IMAP provider only accepts messages up to 25 MB, these emails will be rejected during the migration.
💡 How to fix it: First, try increasing the maximum message size in your IMAP provider’s admin panel and perform a resync by clicking on the “Sync Now” button on the details page.
➡️ If raising attachment limits is not possible, check your migration log for messages that exceeded the size limit, identify the affected messages in your email client, delete the large attachments, and perform a resync („Sync Now“ button) so that the messages are migrated without attachments.
Problem:
Migration Finished With Errors / Not All Data Was Migrated
If your migration has finished with errors, you very likely exceeded Microsoft’s email limits. This can sometime happen when migrating large mailboxes or mailboxes with lots of emails.
💡 How to fix it: Disable Microsoft’s EWS throttling and run a new sync by clicking on the “Sync Now” button on your migration’s details page.
Problem:
Some Folders Are Not Included After the Migration or Resync
It is possible that some custom subfolders aren’t included in the migration or resync. This happens when the respective folders already exist in the target mailbox but aren’t fully subscribed. If this is the case, they are skipped to avoid duplicates. To resolve this issue, go with one of these two options:
💡 Option 1: Delete the affected folders on the target and perform a resync:
Remove the empty or partially-filled folders on your target mailbox (the ones that are missing emails), then start a resync of your existing migration in the MailJerry app. The folders will be recreated and all emails will be copied over.
💡 Option 2: Rename the affected folder on the source and resync:
If you prefer not to delete anything on the target (e.g. because it might contain messages from other sources than your Office 365 account), rename the affected folder in your target mailbox and perform a resync (simply hit the „Sync Now“ button)
Office 365 to IMAP Migration:Frequent Questions
Can I use my Office 365 mailbox during the migration?
Yes! You can continue using both your Office 365 and your new IMAP mailbox to receive, read, and send emails while the migration is in progress. However, we recommend avoiding major structural changes (such as large clean-ups or reorganizations) in either mailbox.
Also, please disable any third-party tools that may interfere with the migration, such as backup tools or active sync applications.
How long does the migration from Office 365 to IMAP take?
This depends on two parameters: The size of your Office 365 mailbox and the transfer speed of your IMAP provider. In general, most IMAP providers don’t apply bandwidth limitations. However, Microsoft may apply throttling that can slow down the migration for large mailboxes.
If this happens, don’t worry – it doesn’t matter if your migration takes a few hours or even days. MailJerry will handle everything automatically. For large mailboxes (10 GB+), consider disabling EWS throttling before starting the migration.
My IMAP account already contains emails. Is this a problem?
No, not at all! Simply proceed with your migration as described in this tutorial. MailJerry will add the emails from your Office 365 account without changing or deleting any data already existing in your IMAP account.
Will my contacts and calendar be migrated automatically?
No. The email migration only move your emails and folders – not your contacts or calendar. You’ll need to migrate them separately. To do so, have a look at these sections on how to migrate contacts and how to migrate calendars.
What happens with emails received in my Office 365 account after the migration?
After the migration, emails received in your old Office 365 account won’t automatically appear in your new IMAP mailbox. To ensure that new emails are synced, activate the auto-sync (synchronizes every three hours for 10 days) or the backup mode (syncs permanently). See Step 04 for instructions.
What’s the difference between the auto-sync and the backup mode?
The auto-sync synchronizes your old account with your new account every three hours for a limited time (10 days). It’s the perfect choice if you plan to delete your old account or change DNS / MX settings.
The backup mode is best suited if you plan to keep your Office 365 mailbox but want all incoming emails forwarded to your new IMAP account permanently. By activating the backup mode, all emails received in your old account will automatically be migrated to your IMAP account – without any time limit.
I need to migrate a large or very large mailbox from Office 365. Any tips?
For sure! This article explains everything you need to know about migrating large amounts of data to or from Microsoft 365 and Exchange Online. Additionally, make sure to disable EWS throttling before starting the migration to avoid interruptions.
