I've been on the IT side of two Lotus Notes-to-Microsoft migrations, and the first thing every admin learns is that the mailboxes are the easy part — it's the twenty-year-old Domino applications nobody documented that bite you. This guide covers the practical routes to get mail and data into Microsoft 365 in 2026, what each method costs you in effort and fidelity, and the pitfalls the tool adverts never mention. A naming note before we start: Lotus Notes is now HCL Notes (HCL bought Domino and Notes from IBM in 2019), and Office 365 is now branded Microsoft 365 — the search terms and the products have both outlived their names.
Quick answer: The two practical methods in 2026 are (1) Microsoft's IMAP-based migration, free but slow and metadata-thin, done from the Domino server side, and (2) dedicated migration suites such as Quest's Migration Suite for Lotus Notes, which move calendars, contacts and archives with far better fidelity for larger estates. Both move mail only — Domino applications need separate replatforming, and NSF-to-PST converters remain an option for one-off mailbox rescues.
Why migrate off Lotus Notes in 2026?
Notes estates still exist because they work — and because the Domino applications built on top of them are business-critical. But the pull toward Microsoft 365 keeps strengthening:
- Licensing and skills: HCL Notes/Domino licences and the shrinking pool of Domino administrators get more expensive every year, while Microsoft 365 bundles mail, files, Teams and Office apps most businesses already use.
- Security patching: a single cloud provider patching Exchange Online is simpler than maintaining Domino servers at current fix packs.
- Hybrid work defaults: Teams, OneDrive and Outlook mobile are where employees already are.
The realistic warning: if you run dozens of custom Domino workflow applications, mail migration is maybe a third of your project. Budget for the apps.
Method 1: IMAP connector migration (free, built-in)
This is the do-it-yourself route using Microsoft's IMAP migration — you expose the Domino mailboxes over IMAP, then Microsoft 365's IMAP mailbox migration pulls mail into cloud mailboxes. Expect it to move emails (and little else) — IMAP doesn't carry calendars, contacts, tasks or journal data.
1. Back up your NSF files. Always. Take a full backup of every mail database before touching the server — corruption mid-migration with no backup is a career event.
2. Create the target mailboxes. Provision (or synchronise) users in Microsoft 365, either manually in the admin centre or via Microsoft Entra Connect if you run directory sync.
3. Enable IMAP on Domino. On the Domino server, open the Domino Administrator → Configuration tab → Server document for the IMAP server → Ports → Internet Ports → Mail, and set the IMAP TCP/IP port to Enabled (port 143 by default — 993 if you're doing TLS, which you should).
4. Set Internet passwords. Each Notes user needs an internet password in their Person document so IMAP can authenticate — the Notes client password alone won't work.
5. Prepare the CSV. Microsoft's IMAP migration uses a CSV listing, per user: target mailbox email address, IMAP server address, source username and password (or an admin credential with full mailbox access).
6. Create the migration batch. In the Microsoft 365 admin centre (Exchange admin → Migration), create an IMAP migration batch, upload the CSV, and start it. Sync is incremental, so you can run it days ahead of cutover.
7. Cut over. When the final sync delta is small, point MX records at Microsoft 365, run a final sync, and complete the batch.
Drawbacks, honestly: mail-only (no calendars/contacts), slower on big mailboxes, per-user credential juggling, and no migration of Notes-specific content. It's the right tool for small, mail-centric estates on a budget.
Method 2: Dedicated migration suites (the enterprise route)
For anything beyond a couple of hundred mailboxes — or any estate where calendars, contacts and archives must arrive intact — purpose-built suites are the standard:
- Quest Migration Suite for Lotus Notes is the long-standing market leader, moving mail, calendars, contacts, tasks and archives with coexistence support (so Notes and Microsoft users can share calendars mid-project) and staging tools for the application inventory.
- Transend Migrator handles NSF → Exchange/Online and NSF → PST conversions, popular for mid-size one-shot projects.
- Binary Tree's tooling, now part of the Quest portfolio, historically served the largest global estates.
These cost real money (per-mailbox licensing) and need a project plan: coexistence design, pilot wave, department-by-department batches, and cutover per wave. That's exactly what you're paying for.
Method 3: NSF to PST conversion (mailbox rescue, not strategy)
For individual mailboxes, departed employees, or legal holds, NSF-to-PST converter tools extract a Lotus Notes database into a PST file you can then import anywhere (including Microsoft 365 via the Import Service, or into Outlook directly). This is a scalpel, not a migration strategy — per-mailbox licensing gets silly at scale, and you still handle the PST import separately. If you go this route, trial the tool on your messiest mailbox before buying.
What no method migrates: the Domino applications
The part of Notes nobody puts in the brochure is the application layer — the custom workflow apps, expense approvals, discussion databases and team spaces built on Domino over fifteen years. Mail migration tools don't touch them. Your real options are: rebuild in Power Apps/SharePoint, move to SaaS equivalents, retire what nobody uses, or keep a Domino server running just for legacy apps. In every Notes migration I've touched, the application inventory was the project's true scope — do that audit first, and the mail migration becomes the simple part.
Pre-migration checklist
1. Inventory everything: users, mailbox sizes, archives, and — above all — Domino applications and their owners.
2. Clean house first: deleting dead mailboxes and stub archives before migration cuts every method's cost.
3. Pilot one department end-to-end, including Outlook profile setup and mobile re-enrolment, before announcing dates.
4. Plan coexistence if the project runs months: free/busy between Notes and Microsoft users matters politically as much as technically.
5. Communicate the cutover: old mail location, new webmail URL, phone re-setup — the tickets you preempt here are half your support load.
For the neighbouring migrations, we have step-by-step guides to import PST files into Thunderbird, import OST data into Gmail, and a review of the best EDB-to-PST converter tools for Exchange-side rescues.
Frequently asked questions
Is Lotus Notes still supported in 2026?
Yes — as HCL Notes and HCL Domino, owned by HCLSoftware since IBM sold the portfolio in 2019. It's actively maintained (with new Domino releases still shipping), so this migration is about economics and ecosystem, not an emergency deadline. The shrinking community of Domino developers and admins is the practical forcing function for most organisations.
Can Microsoft 365 migrate Lotus Notes mailboxes natively?
Partially. Microsoft 365's built-in IMAP migration pulls email from Domino's IMAP service into cloud mailboxes — free and supported, as documented on Microsoft Learn — but IMAP moves mail only: no calendars, contacts, tasks, or Notes application data. Native calendar/contact migration requires third-party migration suites such as Quest's.
What is the fastest method to migrate Lotus Notes to Office 365?
For speed on small estates, the IMAP migration batch with a pre-staged CSV is the fastest free route — a handful of mailboxes syncs in hours. For large estates, Quest's migration suite with parallel migration workers finishes faster overall despite the setup cost, because it moves everything (mail, calendars, archives) in one pass instead of requiring follow-up imports.
Do NSF to PST converters preserve folder structures?
Good converters preserve the folder hierarchy, read/unread flags, and most message metadata; attachments travel as attachments. What frequently suffers: Notes-specific items like custom forms, journal documents and embedded objects render imperfectly in Outlook. Always run a trial conversion on your most complex mailbox and have a user eyeball the result before committing to a tool.
What should we do with old Domino applications after mail migration?
Inventory them first, then sort into four buckets: retire (no one has used it in a year), replace with a SaaS product, rebuild in Power Apps/SharePoint if it's business-critical, or leave on a minimal Domino server as a read-only archive. Don't migrate mail and assume the apps will follow — they won't, and undocumented workflow apps are where Notes projects go to die.
Related reading
- How to import PST files into Thunderbird
- How to import OST data into Gmail
- Best EDB-to-PST converter tools reviewed
I've lived two of these migrations from the admin chair — tell me your user count and how many Domino apps you're running in the comments, and I'll tell you which method fits.
