A 5-minute walkthrough of moving MDaemon Server mailbox data into a Microsoft 365 (Exchange Online) mailbox. Uses the 4n6 MDaemon to Microsoft 365 Migration Tool with modern authentication / OAuth, since Microsoft 365 disabled IMAP basic auth in 2022. MDaemon stores mail in proprietary MSG and MRK files, so a migration tool is needed to bridge the format gap. If you only need a PST archive copy without cloud destination, see our convert MDaemon emails guide. If your destination is Google Workspace instead, see our cloud migration guide pattern.
Video Transcript
Hello and welcome. This video shows how to migrate MDaemon Server mailbox data to a Microsoft 365 account. We use the 4n6 MDaemon to Microsoft 365 Migration Tool. MDaemon stores mail in a proprietary MSG plus MRK file format, distinct from the standard EML or MBOX you might know. Each user mailbox lives in a folder under C:\MDaemon\Users\<domain>\<username>. Inside are subfolders for INBOX, Sent, Drafts, custom folders, plus special MRK container files for AddrBook, Calendar, Notes, TaskList. The 4n6 tool reads all of these.
Step one. Set up Microsoft 365 first. Sign in to admin.microsoft.com, verify your custom domain, assign a Microsoft 365 license to each destination user.
Step two. Stop the MDaemon service briefly so the Users directory is not in flux during the copy. Copy the user folders from C:\MDaemon\Users\domain to a Windows workstation. Restart MDaemon.
Step three. Download and install the 4n6 MDaemon to Microsoft 365 Migration Tool.
Step four. Launch the tool. Click Open MDaemon Configured Account if MDaemon is on the same machine, otherwise Choose Folders and browse to the copied Users directory. The tool reads MSG and MRK files and shows the folder tree. Tick the folders to migrate.
Step five. From the Export tab, pick Office 365. Enter the destination Microsoft 365 email address. Microsoft will prompt for OAuth sign-in in a browser window. Sign in with the destination account credentials and approve the Mail.ReadWrite permission.
Step six. Click Save to start the migration. The tool uploads each message to the M365 mailbox via Exchange Online's modern auth-protected IMAP. A live progress bar shows uploaded count. When complete, a Notepad log lists items migrated, items skipped and any errors. Verify by opening Outlook on the web and checking the message counts match the source MDaemon mailbox. Thanks for watching.
What MDaemon Is and Why You Would Migrate Off It
MDaemon Email Server is a Windows-only mail server developed by MDaemon Technologies (formerly known as Alt-N Technologies, founded 1996). It bundles SMTP, POP3, IMAP, ActiveSync, plus a custom WebMail interface called WorldClient and a calendar/groupware feature set under the "MDaemon Connector for Outlook" branding. MDaemon competes directly with Microsoft Exchange in the Windows-shop SMB market and has historically been popular with Indian SMBs that wanted Exchange-style features without Exchange's licensing complexity.
The most common reasons to migrate off MDaemon to Microsoft 365 in 2026: consolidating to Microsoft's cloud productivity stack (Outlook + Teams + OneDrive), retiring on-premises Windows Server hardware, eliminating the need to manage MDaemon updates and security patches in-house, getting modern collaboration features (shared calendars, distribution lists, online meetings) that MDaemon's WorldClient interface cannot match, or because the company has been acquired and the parent company runs M365.
The tool used in this video is the 4n6 MDaemon to Microsoft 365 Migration Tool. It is a different product from the 4n6 MDaemon Server Converter covered in our convert MDaemon emails guide. The Server Converter outputs PST and other file formats. This Migration Tool uploads directly to Microsoft 365 mailboxes via OAuth.
How MDaemon Stores Mail (Different from Kerio or Exchange)
Understanding MDaemon's storage layout helps the migration go smoothly. Unlike Kerio Connect (which stores standard EML files in a directory tree) or Exchange (which uses a single EDB database), MDaemon uses a hybrid approach: each user has a folder of subdirectories with proprietary MSG files for messages, plus separate MRK container files for non-mail data.
| Component | Location and format |
|---|---|
| User mailbox root | C:\MDaemon\Users\<domain>\<username>\ |
| Mail messages | MSG files (MDaemon proprietary format, NOT Microsoft Outlook MSG) inside subfolders like INBOX, Sent, Drafts, Trash, custom user folders. Each .msg file is a single email. |
| Folder index files | Each mail subfolder contains .mrk companion files holding folder-level metadata: read flags, message ordering, message IDs. These are crucial for reconstructing the folder state during migration. |
| Contacts | AddrBook.mrk: single MRK container file holding all contacts for the user as vCard-equivalent entries. |
| Calendar | Calendar.mrk: single MRK container file holding all calendar events. |
| Notes | Notes.mrk: single container of stored notes. |
| Tasks | TaskList.mrk: single container of tasks and to-dos. |
| Documents | Documents.mrk: for users who store personal documents inside MDaemon (less common). |
| IMAP state | .IMAP folder holds IMAP-specific metadata: subscribed folder list, UIDVALIDITY values, last-seen state. |
| Domain-level data | Public folders, shared resources, server-wide address books live one level up at C:\MDaemon\Users\<domain>\, outside individual user folders. |
This layout matters for two reasons: First, you cannot just copy a single MDaemon MSG file and open it in Outlook (Outlook's MSG format is different despite the same extension). Second, the .mrk container files are essential to extract calendar, contacts, notes and tasks correctly. A basic file copy that grabs only the message folders will lose all non-mail data.
Three Paths from MDaemon to Microsoft 365
For an MDaemon-to-M365 project there are three realistic paths. Pick based on data volume and operational constraints.
| Path | When to pick it |
|---|---|
| Direct cloud upload (this video) | Pick for small to mid-size migrations (under 100 GB total, under 50 users). Uses 4n6 MDaemon to Microsoft 365 Migration Tool. Reads MDaemon Users directory directly, uploads to M365 mailboxes via OAuth-authenticated IMAP. Pros: simplest workflow, no PST intermediate, messages appear live as upload progresses, calendar and contacts handled from .mrk files in same pass. Cons: depends on stable internet through entire upload, OAuth sign-in needed per destination user. |
| PST intermediate + Microsoft Network Upload | Pick for large migrations (100 GB+ or 50+ users). First convert MDaemon to PST using the 4n6 MDaemon Server Converter (see our convert MDaemon emails guide). Then upload PSTs to Microsoft 365 via the free Network Upload service. Pros: bypasses IMAP rate limits, faster for enterprise scale, free Microsoft tool for upload phase. Cons: more administrative steps, requires AzCopy + Azure storage URL. |
| Exchange Online IMAP migration (admin-driven) | Pick when MDaemon is still running and you want Microsoft to pull. Configure MDaemon as IMAP source in Exchange admin center > Migration. Microsoft pulls from MDaemon's IMAP server-side, writes to M365 mailboxes. Pros: free, official Microsoft path, no third-party tool. Cons: requires live MDaemon with IMAP enabled, doesn't migrate calendar (.mrk) or contacts (AddrBook.mrk), slow on large mailboxes, EAC migration UI is fragile. |
Microsoft 365 Tenant Pre-Migration Checklist
The MDaemon side is well-understood by the tool. The M365 destination is where most migrations stumble. Work through this list before clicking Convert.
| Check | Why it matters |
|---|---|
| Microsoft 365 subscription with Exchange Online | Pick a plan that includes Exchange Online (Business Basic, Business Standard, Business Premium, Enterprise E1/E3/E5, or standalone Exchange Online Plan 1 or 2). Plans without Exchange Online cannot accept mail. |
| Custom domain verified | Add yourcompany.com to admin.microsoft.com > Settings > Domains. Verify ownership via DNS TXT record. Domain must be verified before destination users can be created on that domain. |
| Destination users created with matching addresses | Create each MDaemon user as a Microsoft 365 user at admin.microsoft.com. Use the same email address as MDaemon (raj@yourcompany.com on MDaemon = raj@yourcompany.com on M365) so the OAuth sign-in references the right user. |
| Mailbox license assigned per user | Each user needs a license that includes Exchange Online. Without a license, no mailbox is created and migration silently fails. License assignment triggers mailbox provisioning which takes 5-30 minutes. |
| Mailbox actually provisioned | Verify each destination user has a working mailbox by signing them in to outlook.office.com first. If "Welcome to Outlook" page shows, mailbox exists. |
| Modern authentication on (default for new tenants) | Verify at admin.exchange.microsoft.com > Settings. New tenants have it on by default. Old tenants where it was once disabled need it re-enabled. |
| Conditional Access policy review | Some enterprise tenants block third-party migration tools via Conditional Access in Microsoft Entra. SMBs rarely have these policies. If OAuth sign-in fails with "your sign-in was blocked", coordinate with the admin to allow the tool's app ID or temporarily exempt the migrating user. |
| MFA configured for destination users | If destination users have MFA enabled (recommended), the OAuth prompt during migration asks for the MFA challenge. Have the user available with their phone or authenticator app at the moment migration starts. |
| MDaemon Users directory copied off the live server | Stop MDaemon service briefly via services.msc, copy C:\MDaemon\Users\<domain>\ to a Windows workstation, restart MDaemon. Reading the live Users directory while MDaemon is writing produces corrupt MSG/MRK reads. |
| Stable internet connection | Sustained upload over the network. 50 GB on 50 Mbps Indian residential broadband takes roughly 2.5 hours. Wired ethernet, not Wi-Fi, for stability. |
| MX records still pointing at MDaemon | Do NOT change MX records before migration completes. Mail flow stays on MDaemon so no incoming messages are lost. Cutover happens after verification. |
| Trial run with one user first | Migrate one volunteer user end-to-end. Catches issues with licenses, OAuth permissions, MFA prompts, .mrk handling, custom folder names before they hit your bulk job. |
Tool Specifications
| Specification | Value |
|---|---|
| Tool name | 4n6 MDaemon to Microsoft 365 Migration Tool |
| Vendor | 4n6 Software (forensiksoft.com) |
| Trial limit | 10 items per folder, free download |
| Operating system | Windows 7 / 8 / 8.1 / 10 / 11 (32 or 64-bit), Windows Server 2008 / 2012 R2 / 2016 / 2019. Migration tool is Windows-only. |
| Source MDaemon versions | MDaemon Server 12.x through 23.x. All recent MDaemon Email Server releases. |
| Source data access | Read access to MDaemon Users directory (default C:\MDaemon\Users\<domain>\). Local copy, network share or USB drive all work. Auto-detect feature works when MDaemon is installed on the same machine. |
| Destination | Microsoft 365 (any plan with Exchange Online), standalone Exchange Online Plan 1/2, or hosted Exchange Server 2016/2019/2022. |
| Destination authentication | OAuth 2.0 / Modern Authentication. Tool opens a browser sign-in window and uses XOAUTH2 to authenticate the IMAP upload. |
| File formats parsed | MSG (MDaemon proprietary), MRK, AddrBook.mrk, Calendar.mrk, Notes.mrk, TaskList.mrk, Documents.mrk, .IMAP folder contents. |
| Migration types supported | Emails, calendar events, contacts, tasks, notes, journals, attachments. Multi-user batch mode. Selective folder migration with date filters. Auto-detect configured MDaemon profile. |
| RAM | 2 GB minimum, 4 GB recommended for large mailboxes |
| Internet | Required throughout the upload. Wired ethernet recommended. |
6 Steps to Migrate MDaemon to Microsoft 365
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Set up Microsoft 365 destination first. Sign in to admin.microsoft.com. Verify your custom domain at Settings > Domains via DNS TXT record. Create destination users at Users > Active users with the same email addresses as their MDaemon accounts. Assign a Microsoft 365 license that includes Exchange Online to each user. Wait 5-30 minutes for mailboxes to provision. Verify by signing in as a destination user at outlook.office.com.
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Copy the MDaemon Users directory to a Windows workstation. On the MDaemon server, open services.msc and stop the MDaemon service so the Users directory is not in flux during the copy. Copy C:\MDaemon\Users\<domain>\ to your Windows workstation (use robocopy or rsync for resumable, verified copies). Restart the MDaemon service after the copy completes so users keep getting mail during the upload phase. Migration runs against the copy, not the live store.
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Install the 4n6 MDaemon to Microsoft 365 Migration Tool. Download the installer from forensiksoft.com. Install on the Windows workstation. The tool is standalone and does not require MDaemon, Outlook or any Microsoft client to be installed. Trial version migrates 10 items per folder so you can verify the workflow before buying a license.
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Load MDaemon mailbox and select folders. Open the converter. If MDaemon is installed on the same machine, click Open MDaemon Configured Account Data for auto-detection. Otherwise click Choose Files or Choose Folders and browse to the copied Users\<domain>\<username>\ directory. The tool reads MSG files, MRK container files (AddrBook.mrk, Calendar.mrk, Notes.mrk, TaskList.mrk, Documents.mrk), and the .IMAP folder. The folder tree appears on the left panel. Tick the folders to migrate. Use the preview pane (Hex, Raw, Headers view modes) to inspect individual messages.
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Pick Office 365 and authenticate via OAuth. From the Export tab, pick Office 365. Enter the destination Microsoft 365 email address. Click Save. Microsoft opens an OAuth sign-in prompt in your browser. Sign in with the destination account credentials. If MFA is enabled, complete the MFA challenge with your authenticator app. When prompted, approve the Mail.ReadWrite permission for the migration tool. The browser closes and the tool proceeds.
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Click Save and verify in Outlook on the web. Migration starts. The tool uploads each parsed message to the Microsoft 365 mailbox via Exchange Online's modern auth-protected IMAP endpoint. Calendar events from Calendar.mrk go to the Outlook calendar, contacts from AddrBook.mrk go to People, tasks from TaskList.mrk go to Tasks. A live progress bar shows uploaded count per data type. When complete, a Notepad log lists items migrated, items skipped and any errors. Sign in to outlook.office.com as the destination user and verify each data type.
Common Errors and Fixes
| Error or symptom | Cause and fix |
|---|---|
| "Cannot read MSG file" or "Invalid MSG header" | The MDaemon Users directory was copied while MDaemon was still running and writing to a file. Stop MDaemon service, re-copy that user's folder, retry. Alternatively the MSG file is genuinely corrupt, so skip it and check the MDaemon server logs for delivery errors around its timestamp. |
| OAuth sign-in fails with "your sign-in was blocked" | Conditional Access policy in Microsoft Entra is blocking the migration tool's app. An admin needs to allow the tool's app ID, exempt the migrating user, or temporarily disable the policy. Common in enterprise tenants with strict Microsoft Entra security configurations. |
| "Mailbox not found" or "User does not have a mailbox" | Microsoft 365 license is not assigned, or the license was assigned recently and the mailbox is still being provisioned. Check at admin.microsoft.com > Users > user. License must include Exchange Online. After assignment, wait 30 minutes and verify by signing in to outlook.office.com as that user. |
| Calendar.mrk events appear as plain emails in Inbox | The tool wrote calendar items as mail messages. Re-run the conversion separately for just Calendar.mrk with output set to ICS, then import the ICS file into the destination user's calendar via outlook.office.com > Calendar > Import calendar. Same approach for AddrBook.mrk → vCard → import to Contacts. |
| "Authentication failed" using app password | App passwords don't work for Microsoft 365 work or school accounts. Microsoft removed IMAP basic auth (and therefore app password support for IMAP) in late 2022. Use OAuth via the tool's browser sign-in prompt instead. App passwords still work for personal @outlook.com / @hotmail.com but those are rarely the destination for SMB migrations. |
| MFA prompt times out during migration | The OAuth flow expects the user to complete MFA within ~60 seconds. Coordinate with each destination user to be available at their authenticator app at the start of their migration. For bulk migrations, schedule per-user authentication windows. |
| Upload stalls after a few hundred messages | Hit Exchange Online's IMAP throttle. M365 imposes per-mailbox connection and message rate limits. The tool throttles automatically and resumes. For large mailboxes plan to run overnight. If progress stops entirely for over 30 minutes, restart the tool, which should resume from where it left off based on the destination mailbox state. |
| "Message size exceeds 150 MB" | Exchange Online has a 150 MB per-message size limit. MDaemon MSG files with attachments larger than this skip silently. Check the conversion log for "size exceeded" entries. For these messages, extract attachments separately and upload via OneDrive with a sharing link in the email body. |
| "Mailbox storage quota exceeded" | Default Exchange Online mailbox quota is 50 GB on M365 Business plans, 100 GB on E3+ plans. If an MDaemon user mailbox is 80 GB, migration cannot complete on Business Standard. Check current quota at admin.exchange.microsoft.com > Recipients > Mailboxes > user. Upgrade to E3+ or split data across primary mailbox + In-Place Archive (50 GB additional on E3+). |
| Custom folder names with special characters disappear | Some MDaemon folder names use slashes, colons or non-ASCII characters that don't translate to Outlook folder names. The tool sanitises by replacing offending characters with underscores. Check the log for "renamed" entries and verify the renamed folders match expectations in Outlook. |
| Connection drops mid-migration | Indian residential broadband often has 5-30 second drops on Wi-Fi. Use wired ethernet. If drops continue, split migration into per-folder batches. Smaller batches mean smaller restarts when the connection breaks. |
PST Intermediate Path (When This Is Better)
For migrations over 100 GB total or 50+ users, the PST-intermediate path via Microsoft's free Network Upload service is often faster and more reliable than direct cloud upload.
| Phase | What happens |
|---|---|
| 1. Convert MDaemon to PST locally | Use the 4n6 MDaemon Server Converter to convert MDaemon Users data to PST files, one per user. See our convert MDaemon emails guide. Output: a directory of PST files like raj@yourcompany.com.pst. |
| 2. Get Azure storage SAS URL | In Microsoft Purview compliance portal > Data lifecycle management > Microsoft 365 > Import, click New import job. Pick Upload your data. The wizard provides a one-time SAS (Shared Access Signature) URL to a Microsoft-managed Azure Storage container. |
| 3. Upload PSTs with AzCopy | Download AzCopy v10 from Microsoft. Run azcopy.exe copy with the PST folder as source and the SAS URL as destination. AzCopy uploads PSTs in parallel, resumes on failure, and is much faster than IMAP because it bypasses message-level rate limiting. |
| 4. Create CSV mapping file | Build a CSV mapping each PST file to a destination M365 user mailbox per Microsoft's Network Upload documentation template. |
| 5. Submit import job | Submit the CSV in Purview. Microsoft analyses uploaded PSTs and shows a preview. Approve. Microsoft writes PST contents into destination mailboxes server-side (no IMAP rate limits). Typical throughput: 24-72 hours for ~500 GB. |
| 6. Verify and clean up | After completion, verify message counts in destination mailboxes via Outlook on the web. Microsoft auto-deletes the temporary Azure container 30 days after job completion. |
When to pick PST intermediate: total MDaemon data over 100 GB, more than 50 users, internet connection unreliable, you also need a PST archive copy for compliance, you have a global admin willing to drive the Microsoft Purview workflow.
MX Record Cutover to Microsoft 365
The mail-flow cutover is similar to other M365 migrations.
| Phase | What happens |
|---|---|
| Before migration | MX records point to MDaemon. All mail flows to MDaemon. Migration tool uploads historical mail to M365 mailboxes in parallel. No mail flow change yet. |
| Migration in progress | Run the 4n6 MDaemon to Microsoft 365 Migration Tool for all users. Mail still flowing to MDaemon. Plan for a Friday-night start so it finishes by Sunday. |
| Verification phase | Sign in to each destination M365 mailbox at outlook.office.com. Verify message count, folder structure, calendar events, contacts. Have each user verify their own mailbox if possible. |
| MX cutover | Update DNS MX records at your registrar. Set primary MX to <yourdomain>-com.mail.protection.outlook.com with priority 0. Actual hostname shown in admin.microsoft.com > Settings > Domains > your domain > DNS records. Set TTL to 300 seconds a day before for fast propagation. |
| Cutover window | For 24-48 hours, mail can land at either MDaemon or M365 as DNS propagates. Configure MDaemon to forward all incoming mail to the M365 domain so nothing is lost during the propagation gap. After full propagation, mail flows only to M365. |
| Post-cutover | Keep MDaemon running read-only for 30-90 days as a safety net. Decommission MDaemon Server once you're confident no missed mail remains. |
Tool Comparison: MDaemon to Office 365 Migration Options
| Tool | Notes |
|---|---|
| 4n6 MDaemon to Microsoft 365 Migration Tool (this video) | Direct OAuth-authenticated cloud upload to Exchange Online. Trial: 10 items per folder. Windows only. Sister products: 4n6 MDaemon Server Converter (PST output), 4n6 MDaemon to Gmail Migration (Workspace destination), 4n6 MDaemon to IMAP Migration (generic IMAP destination). |
| Microsoft Network Upload (free) + 4n6 MDaemon Server Converter | Two-tool combination. Free Microsoft Network Upload service plus the PST conversion via 4n6 Server Converter. Best for 100 GB+ migrations. Documented at Microsoft Learn: Use Network Upload to Import PST Files. |
| Exchange Online IMAP migration (admin-driven) | Free, official Microsoft path. Configure MDaemon as IMAP source in Exchange admin center > Migration. Microsoft pulls. Pros: free. Cons: requires live MDaemon with IMAP enabled, doesn't handle calendar (.mrk) or contacts (AddrBook.mrk), slow on large mailboxes. |
| RecoveryTools MDaemon Migrator | Similar pricing range to 4n6. Cloud destination support including M365, Workspace, Yahoo, Outlook.com. Trial: 25 items per folder. Windows only. |
| BitRecover MDaemon Converter | ~$89 starter price. 25+ saving formats including direct M365 upload. 30-day money-back guarantee. |
| SysTools (no dedicated MDaemon-to-O365 product) | SysTools does not ship a dedicated MDaemon-to-Office 365 migration tool. Their SysTools IMAP Migration tool can be used when source MDaemon is live with IMAP enabled. Cleaner option is to use a vendor with native MDaemon MSG/MRK parsing. |
Real Migration Scenarios
| Scenario | Approach and notes |
|---|---|
| SMB retiring on-premises MDaemon, 20-50 users to M365 Business Standard | The most common case in Indian SMBs. Total Users data 30-200 GB. Direct cloud upload with the 4n6 MDaemon to M365 tool. Plan one weekend of upload. Each user authenticates via OAuth at the start of their migration. Schedule per-user authentication slots. |
| MDaemon Connector for Outlook users | Shops that use MDaemon Connector for Outlook (the proprietary Outlook plugin that gives MDaemon Exchange-like features) often have rich calendar and shared-folder usage. The 4n6 tool migrates calendar, contacts and tasks via the .mrk files. For shared folders, migrate them as Microsoft 365 shared mailboxes manually. |
| Large enterprise migration, 200+ users, 1+ TB total | PST intermediate via Microsoft Network Upload. Convert MDaemon to PST overnight using the 4n6 MDaemon Server Converter, then upload PSTs via AzCopy to Azure storage, then submit a Network Upload job. Microsoft's server-side import is much faster than IMAP at this scale. Allow 1-2 weeks total. |
| Phased hybrid migration: pilot users first, rest later | Migrate IT and management first as a pilot. Verify M365 setup works end-to-end before bulk. During hybrid period, set MDaemon to forward mail for migrated users to their M365 addresses. Roll out remaining users in batches over 2-4 weeks. MX cutover happens after everyone migrates. |
| Domain rebrand: MDaemon on oldcompany.com, M365 on newcompany.com | Map source mailbox to destination email per user. For each user, sign in as new@newcompany.com when prompted. Set up forwarding on the M365 side so old@oldcompany.com routes to new@newcompany.com during transition. |
| Departed-employee archive into shared M365 mailbox | When an employee leaves, migrate their MDaemon mailbox into a shared mailbox in M365. HR or the manager retains access. Allows compliance access without paying for a per-user license long-term. |
| MDaemon hosted by a managed service provider | If your MDaemon is hosted by an MSP with no file-system access, you cannot copy the Users directory. Fall back to the Exchange Online IMAP migration path (admin-driven, server-to-server) using MDaemon's IMAP credentials. Calendar and contacts won't migrate this way, so handle separately by exporting from MDaemon WorldClient and importing to M365. |
đź’ˇ Pro tips for MDaemon to Office 365 migrations
- Run migration before MX cutover, never after. Mail flow stays on MDaemon during migration so historical mail uploads while no new mail is lost. Cut over MX only after verification.
- Make sure .mrk container files are included in the copy. A simple mail-folder-only copy misses Calendar.mrk, AddrBook.mrk, Notes.mrk, TaskList.mrk and loses all non-mail data. Copy the entire user folder, not just the mail subdirectories.
- Coordinate per-user OAuth authentication slots. Each destination user has to be at their phone to complete MFA at the moment their migration starts. For bulk migrations, schedule a 5-10 minute window per user. Or migrate one user at a time.
- Use robocopy or rsync for the Users directory copy. Both verify integrity and resume on failure. Plain Explorer drag-and-drop can silently skip files on permission errors.
- Wired ethernet on the migration workstation. Sustained IMAP uploads to Exchange Online are sensitive to connection drops. Indian Wi-Fi on residential broadband often has 5-30 second outages that break the session.
- Pre-create destination mailboxes 30 minutes before migration. License assignment triggers mailbox provisioning but it takes time. Assign licenses early, verify each user can sign in to outlook.office.com, then start migration.
- Use the PST intermediate path for migrations over 100 GB. Microsoft Network Upload is free and bypasses IMAP rate limits.
- Verify quota before migration. Default mailbox quota is 50 GB on M365 Business plans, 100 GB on E3+. If an MDaemon mailbox exceeds the destination quota, upgrade the user's plan or split data across mailbox + In-Place Archive.
- Plan MX cutover for off-hours. Most Indian SMBs prefer Friday-night start so the upload runs over the weekend and Monday morning users are on M365.
- Keep the MDaemon Users directory for 90+ days. If a user reports missing email after migration, you can re-extract from the original.
- If your destination is Google Workspace instead, use the 4n6 MDaemon to Gmail Migration tool. Different OAuth flow, different rate limits. The next companion video in this series covers that path.
- If you only need a PST archive without cloud destination, see our convert MDaemon emails guide.
Frequently Asked Questions
Why is a third-party tool needed for MDaemon to Microsoft 365 migration?
MDaemon stores mail in a proprietary MSG plus MRK file format inside a custom Users directory. Microsoft 365 only accepts mail via standard protocols (IMAP, EWS, Graph API) with modern authentication. There is no native MDaemon export feature that produces a Microsoft-compatible format directly. A migration tool reads MDaemon's proprietary files and uploads them to the M365 mailbox via OAuth-authenticated IMAP, bridging the format gap. The 4n6 MDaemon to Microsoft 365 Migration Tool handles this in one pass.
Can I use IMAP with username and password to migrate to Microsoft 365?
No. Microsoft permanently disabled IMAP basic authentication in Exchange Online for all tenants in late 2022 as part of the multi-year basic auth deprecation. Any migration tool that needs to write to a Microsoft 365 mailbox via IMAP must use OAuth (modern authentication). The 4n6 tool handles this automatically with a browser-based OAuth sign-in prompt when you start the migration.
Where does MDaemon store mailbox data?
MDaemon stores each mailbox under C:\MDaemon\Users\<domain>\<username>\ on the MDaemon server. Inside each user folder are mail subfolders (INBOX, Sent, Drafts, custom folders) containing MSG files, plus special MRK container files for non-mail data: AddrBook.mrk for contacts, Calendar.mrk for calendar events, Notes.mrk for notes, TaskList.mrk for tasks, Documents.mrk for stored documents. The .IMAP folder holds IMAP-specific state. MDaemon is Windows-only so the path is always under C drive (or wherever the admin chose to install).
What is the difference between cloud-direct migration and PST intermediate?
Cloud-direct (this video) reads MDaemon MSG/MRK files and uploads directly to M365 mailboxes via OAuth-authenticated IMAP. Best for under 100 GB total. PST intermediate uses the 4n6 MDaemon Server Converter to first produce PST files, then upload via Microsoft's free Network Upload service in the Purview portal. Best for 100 GB+ migrations because it bypasses IMAP rate limits. See our convert MDaemon emails guide for the PST conversion phase.
How does the migration handle calendar, contacts, and tasks?
MDaemon stores calendar in Calendar.mrk, contacts in AddrBook.mrk, notes in Notes.mrk, tasks in TaskList.mrk inside each user's directory. The 4n6 tool detects these files and writes them to the matching Outlook calendar, contacts, notes and tasks folders in the destination M365 mailbox. Verify after migration by opening Outlook on the web: events appear in the Calendar tab, contacts in People, tasks in Tasks. If any item type appears as plain emails in the Inbox, re-run the conversion separately for that .mrk file with output set to ICS or vCard.
Should I migrate or change MX records first?
Migrate first, change MX records last. Run the migration tool while MDaemon is still receiving mail so no incoming messages are lost. Verify all historical mail has uploaded to Microsoft 365 mailboxes. Only after verification, schedule a maintenance window to update DNS MX records pointing to Microsoft's MX endpoint at <yourdomain>.mail.protection.outlook.com (the actual hostname is shown in the M365 admin center after domain verification). DNS propagation typically takes 1-4 hours.