Migrate HCL Domino to Microsoft 365: Complete Migration Guide

If your company still runs mail on HCL Domino, sooner or later someone will ask when you plan to move to the cloud. Licensing renewals, a shrinking pool of Notes administrators, and the pull of Teams and SharePoint all push in the same direction. The best thing is that you can migrate HCL Domino to Microsoft 365 without losing mail, and you do not need a weekend of panic to do it. The catch is that Domino is not a plain mail server, so the plan has to account for things a standard mailbox move never touches.

This guide walks through the three realistic ways to handle the job, what each one can and cannot carry across, and how to cut over without breaking mail flow. It applies whether you are migrating from HCL Domino (Lotus Notes) to Microsoft 365 for 20 users or 2,000.

Why Teams Migrate HCL Domino to Office 365

• Collaboration tools in one place: Outlook, Teams, OneDrive and SharePoint share one identity, so chat, files and calendars stop living in separate silos.
• Less server upkeep: There are no Domino servers to patch, no replication schedules to babysit and no NSF files to compact.
• Easier hiring: Finding people who know Outlook and the Microsoft 365 admin center is far simpler than finding Notes specialists.
• Better mobile and remote access: Users get the same mailbox on a phone, a browser or a desktop client without a VPN.
• Centralised security: Conditional access, MFA, retention labels and audit logs are managed from one console.

What to Sort Out Before You Migrate

• Take inventory: Export the Domino Directory to a spreadsheet: user names, internet addresses, mail file paths and mail file sizes. The size column tells you how long each batch will really take.

• Find the hidden mail: Local archives, replicas on laptops and mail-in databases rarely show up on the server list. Ask users where their archive NSF files live.

• Decide what happens to encrypted mail: Messages encrypted with a Notes ID can only be read by that user. Plan for them to be decrypted before the move.

• Create the Microsoft 365 side: Add users, assign licences and confirm every user has a mailbox. Verify your domain in the tenant.

• Lower the DNS TTL: Drop the TTL on your MX record to a few minutes at least 48 hours before cutover, so the switch takes effect quickly.

• Back up everything: Keep a copy of every NSF file and the Domino Directory. Do not touch the source until you have verified the destination.

• Pilot with a few mailboxes: Pick a mix: a light user, a heavy user with 20 GB of mail, and someone with a lot of calendar entries.

Methods to Migrate HCL Domino to Microsoft 365

There is no single right method to migrate data. Your data volume, your need for calendars and contacts, & your timeline decide which method suits you.

Method 1: IMAP Migration Batch

This is the Microsoft route. Exchange Online connects to your Domino server via IMAP. Pulls mail into the matching Microsoft 365 mailbox. Follow the steps to perform the migration:

1. On the Domino server, make sure the IMAP task is running & that your users’ mail files are enabled for IMAP. Each person also needs an Internet password in their Person document.
2. Confirm the IMAP service is reachable from the internet on port 993 (SSL/TLS) or 143, and that the server presents a valid, trusted certificate.
3. In the Microsoft 365 admin center, create the user accounts and assign licences.
4. Open the Exchange admin center and go to Migration.
5. Create an IMAP migration endpoint. Enter the Domino server name, port and encryption setting, then test the connection.
6. Prepare a CSV file with three required columns: EmailAddress, UserName and Password. Each row maps a Microsoft 365 mailbox to its Domino login.
7. Create a new migration batch, choose IMAP migration, select the endpoint and upload the CSV.
8. Start the batch and watch the status. Failed rows show an error you can act on.
9. When the sync completes, switch the MX record and complete the batch.

Disadvantages of Manual Method:

• It moves mail only. Calendars, contacts, tasks and journal entries stay behind.
• Domino has no easy administrator-level IMAP login, so you typically need each user’s Internet password or a temporary reset.
• Microsoft documents limits on item count and item size for IMAP migrations, so very large or oversized messages may be skipped. Check the current figures before you start.
• Local archives never travel, because they are not on the server.
• Encrypted Notes messages arrive unreadable or not at all.

Method 2: Convert NSF to PST, Then Import

The second route treats each mail file as a data source rather than a live mailbox. You convert the NSF files to PST format and load the PST files into Exchange Online.

The general flow:

1. Collect the NSF files from the Domino server and from user machines.
2. Convert each NSF to PST. You can export through the Notes client, or use a converter that reads NSF files directly. Our walkthrough on how to migrate Lotus Notes to Outlook covers the conversion side in detail, and opening an NSF file in Outlook explains why NSF files cannot simply be attached to Outlook as they are.
3. Open the resulting PST in Outlook and drag folders into the Microsoft 365 mailbox, or use the Microsoft Purview import service for bulk loads.
4. Compare folder counts between source and destination.

This approach works well when you need calendars and contacts, when you are dealing with archives, or when the Domino server is already switched off. The trade-off is time: converting and loading hundreds of files takes planning, and each PST needs checking.

Method 3: Professional Way to Migrate HCL Domino to Microsoft 365

How to Migrate HCL Domino to Office 365 in Simple Steps:

1. Install the tool on a Windows machine that can reach the Domino server, & pick IMAP as the source.
2. Enter the Domino hostname, the IMAP port, the user’s email address and their Internet password.
3. Wait for the folder tree to load, then browse it to confirm you are in the right mailbox.
4. Tick the folders you want. Take a PST backup first if you want a safety copy.
5. Choose Microsoft 365 as the destination and sign in to the target user’s account.
6. Start the process, watch progress, then repeat for the next mailbox.

Treat it like the IMAP route when it comes to scope. Since it reads mail over IMAP, calendars, contacts and local archives still need the NSF to PST route. It also still needs the IMAP service enabled on Domino and a working Internet password for each user. Test it on one pilot mailbox first and compare the results before you start on the bulk run.

If your goal is mail alone and you can collect the Internet passwords, either IMAP route works, and Cigati IMAP Backup Tool spares you the endpoint and batch setup while giving you a PST backup on the side. If you also need calendars, contacts and archives, the NSF to PST route is the safer fit. When you are moving many accounts at once, the planning advice in our guide to migrating multiple email accounts to Office 365 is worth a read, since the batching logic is similar regardless of the source system.

Domino-Specific Problems to Plan For Migrating from HCL Domino to Microsoft 365

• Encrypted mail: Notes encryption is tied to the user’s ID file. Ask users to decrypt important messages beforehand, or use a method that accepts the ID file during conversion.
• Doclinks: A Notes doclink points to a document inside a Notes database. After migration it will not open. Tell users now so they are not surprised later.
• Rich text formatting: Notes rich text can include embedded objects, tables and inline images. Most of it converts cleanly, but sample a few complicated messages.
• Groups and mail-in databases: Domino groups map best to distribution lists or Microsoft 365 groups, and mail-in databases such as a shared helpdesk inbox map to shared mailboxes. Room and resource reservations become room and equipment mailboxes.
• Domino applications: Workflow databases do not move with mail. Decide whether to rebuild them with SharePoint lists, Power Apps or Teams, or retire them.

Cutover: DNS and Mail Flow

Once your pilot and bulk batches look right, move the mail routing.

1. Point the MX record to your Exchange Online Protection address (it looks like yourdomain-com.mail.protection.outlook.com).
2. Add the Autodiscover CNAME record pointing to autodiscover.outlook.com.
3. Update the SPF record to include spf.protection.outlook.com.
4. Turn on DKIM signing for the domain in the Microsoft 365 Defender portal.
5. Send test messages in both directions, that include to external addresses at Gmail and Yahoo, and check that nothing lands in spam.
6. Run a final incremental sync to catch anything that arrived during the switch.

During a phased migration, keep Domino routing in place for users who have not moved yet, so mail for both groups keeps flowing.

Post-Migration Validation

Do not decommission anything until you have checked the results.

• Compare item counts per folder between the NSF and the new mailbox.
• Open a sample of messages with attachments, inline images and long threads.
• Confirm that received dates in Sent Items & Inbox match the original.
• Check that recurring meetings land on the right days and time zones.
• Review the migration report for skipped or failed items and chase every one.
• Keep the Domino server and NSF backups available, read-only, for 30 to 90 days.

Mistakes That Cause the Most Rework

• Skipping the pilot batch and discovering authentication problems on 200 mailboxes at once.
• Forgetting local archives, then hearing from users a week later that years of mail are missing.
• Cutting over MX records without lowering the TTL first.
• Running two overlapping jobs against the same mailbox, which creates duplicates.
• Deleting the source too early.

Final Thoughts

Migrate HCL Domino to Microsoft 365 is less about the copy and more about preparation. If you inventory your mail files, decide how to handle encrypted messages and archives, pilot with a handful of mailboxes and validate before you decommission, the migration is quite manageable. Choose IMAP when you only need mail, either through Microsoft’s batch or through Cigati IMAP Backup Tool if you prefer a desktop workflow with a PST backup. Whichever way you go, take backups first and keep Domino alive until the last user confirms their data is complete.

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