Legacy Outlook for Mac ends in October 2026: what to export before it does

Legacy Outlook for Mac stops working against Exchange Online mailboxes in October 2026, because the Exchange Web Services it relies on retires on 1 October 2026. The new Outlook for Mac cannot import or export OLM files, which puts it on the wrong side of a split that runs through every Mac email client. Anything sitting in On My Computer folders needs exporting before you switch or it goes nowhere.

Most of this transition is uneventful. Server mail is server mail and it downloads again on the other side once you sign in. The problem is the mail that was never on the server. The client you are moving to also has no way to take an archive file back.

There is enough time to do this properly before October. There is not enough time to do it twice.

What changes for legacy Outlook for Mac in October 2026

Legacy Outlook for Mac talks to Exchange Online through Exchange Web Services or EWS. Microsoft is retiring that service on 1 October 2026. The client has no other way to reach an Exchange Online mailbox. When the service goes, mail delivery to the legacy client goes with it.

The new client is unaffected because it never used EWS. Microsoft describes it as connecting through its own sync technology rather than the old SOAP based API. It points third party developers at Microsoft Graph as the replacement. Nothing you do in Outlook changes which protocol is in play. The client decides.

Nothing is deleted. Your mailbox carries on existing in Microsoft 365 exactly as before. What stops is one particular application's ability to reach it. Webmail, your phone and the new client all keep working throughout.

In practice the client stops sending and receiving. Calendar and contacts stop syncing at the same time, because they travel over the same service. The application still opens and the mail already downloaded is still there to read. So the failure looks partial rather than total. That makes it easy to ignore for a week.

The new Outlook for Mac has shipped for four years. Microsoft puts adoption above 95 per cent, so most people made this move a while ago without noticing. The ones still on legacy are there for a reason. That reason is nearly always a pile of local folders.

Which end of support date applies to your licence

There is more than one deadline. Which one you get depends on your licence and where the mailbox is hosted.

The 2029 dates come with a condition. Legacy Outlook receives security updates only through 9 October 2029. Technical support runs on a best effort basis. Treat those as a longer runway rather than a reprieve.

Microsoft does not split the Office LTSC 2024 row by mailbox type, so treat that date with care. The Exchange Web Services retirement lands on 1 October 2026 whatever licence you hold. An Exchange Online mailbox loses the legacy client on that date either way.

1. Now Until 30 September 2026 Legacy Outlook works normally. Export while the Export button is still there.
2. The cutoff 1 October 2026 Exchange Web Services retires. Legacy Outlook stops reaching Exchange Online mailboxes.
3. On-premises only 9 October 2029 Legacy Outlook stops for on-premises mailboxes too. Security updates only until then.

Why some pages still say October 2025

University IT notices and older forum answers put this deadline at October 2025. A few still do. Microsoft moved it. The current date from Microsoft is October 2026 for Exchange Online, tied to the Exchange Web Services retirement on 1 October 2026.

Treat any page carrying the 2025 date as stale rather than as a second deadline you missed. Nothing was cut off last year.

If your mailbox is on an on-premises Exchange server

Read quickly, the headlines suggest everyone loses legacy Outlook this October. Only Exchange Online connectivity stops in October 2026. An on-premises mailbox keeps working in legacy Outlook for Mac until 9 October 2029, with security updates only and best effort support in the meantime.

Forum threads going back years say the new Outlook for Mac cannot reach an on-premises server at all. That is now out of date. Microsoft lists Exchange Server mailboxes as fully supported in Outlook for Mac, subject to four conditions.

• Exchange Server 2016 or later. Older servers are out.
• NTLM or Basic authentication. Kerberos and certificate authentication are not supported.
• A volume licence or an enterprise or business Microsoft 365 plan. Personal subscriptions do not qualify.
• Office downloaded from the Microsoft 365 portal. The App Store build does not support it.

That last condition catches people out. A Mac set up from the App Store looks identical and will refuse the account, so check where the copy came from before assuming the feature is broken.

Apple Mail on macOS breaks on the same date

This part gets almost no coverage. It catches the people who thought they had already escaped by leaving Outlook.

Read more: What Apple Mail Export Mailbox actually produces.

The retirement is of a service, not of one application. Any client reaching Exchange Online over EWS stops on the same date and Apple Mail on macOS is one of them. Microsoft's message centre notice to tenant administrators, quoted in Apple's own support forum, lists Apple Mail for Mac by application ID among the EWS applications on a tenant. The same notice says Microsoft is working with Apple and suggests moving to Outlook for Mac in the meantime.

Administrators can see this early. Microsoft's Baseline security mode blocks EWS ahead of the global change. Admins who have switched it on report the Exchange account in macOS Mail failing immediately while the same account on iPhone carries on working.

If you moved from Outlook to Apple Mail to dodge this, check again. An Exchange account in macOS Mail is on the same clock as legacy Outlook. Mail on iPhone and iPad appears to be unaffected, though reports on that are not fully consistent, so treat the Mac as the machine at risk.

How to tell if you are running legacy Outlook for Mac

This trips up more people than the deadline itself, because both clients are called Outlook and both carry the same icon. Where the switch lives has also moved. In Office for Mac 16.58 and later it sits under Help, not in the main window.

• Help shows Revert to Legacy Outlook. You are on the new client.
• A Legacy Outlook toggle is switched on. You are on legacy and the deadline applies to you.
• Neither appears anywhere. Either the build predates the toggle or your licence has no route back. Check Help then Check for Updates first.

A second tell sits on the Tools tab. Legacy has Export and Import buttons there and the new client has neither, so if you can see Export you can still get your data out.

If you are on the new client and never deliberately switched, an administrator moved you or the app updated into it. Either way the local folders question below still needs answering, because the data did not go anywhere. It is sitting in a profile the new client cannot read.

What the new Outlook for Mac cannot do

Switching clients is a toggle. Getting your data across is not. Two things go wrong repeatedly.

The new Outlook for Mac cannot import an OLM file

Microsoft documents OLM export and import for the legacy client alone. In the new Outlook for Mac the Import option is greyed out, which is a recurring complaint on Microsoft's own community forums. People export an archive as instructed, switch, then discover there is no way to put it back.

So an OLM export is worth doing, but understand what an OLM file actually is. It is a copy you can keep and read with something else later. It is not a file you can hand back to the new client.

On My Computer folders are local only

Legacy Outlook lets you keep folders under On My Computer. Those live on your Mac and the server has never held them. Rules that filed mail there, archives dragged out of the inbox years ago, anything imported from an old PST all sit in that category.

Check this before anything else. If On My Computer folders are hidden, open Outlook and go to Preferences then General. Clear the Hide On My Computer folders option. What appears is the mail that will not come back on its own.

Comes back on its own

No action needed

• Inbox and every server side folder
• Sent, Drafts, Archive and Deleted Items
• Calendar and contacts held in the account
• Attachments on server side messages

Needs exporting first

Gone if you skip it

• Everything under On My Computer
• Mail imported from an old PST or OLM
• Local folders that rules filed into
• Signatures and client side rules

What to export from legacy Outlook before you switch

Work through these in order. The first two take minutes and tell you whether the rest matters.

1. Unhide On My Computer and look. Empty means the job is small. Full means everything below applies to you.
2. Note what is there. Folder names and rough message counts per folder. You will want these to check the export afterwards.
3. Export an OLM archive. Steps below. Include local folders, contacts, calendars and notes rather than mail alone.
4. Move the OLM off the Mac. An archive on the same disk as the mailbox is one accident away from being nothing.
5. Open the archive with something before you trust it. An export that failed halfway still produces a file. The file still has a size.
6. Only then switch. Toggle off Legacy Outlook, sign in, let the server mail come down.

How to export an OLM file from legacy Outlook for Mac

The export lives on the Tools tab.

1. Open legacy Outlook for Mac, go to the Tools tab and choose Export.
2. In the Export to Archive File (.olm) box, tick every item type you want. Mail, contacts, calendar and notes are separate ticks.
3. Choose Continue.
4. In Save archive file as, pick a location and select Save.
5. Wait for the notification, then choose Finish.

No Export button on the Tools tab means the app is out of date. Go to the Outlook Help menu and click Check for Updates. On some builds the option sits on the File menu instead.

OLM is the only export format legacy Outlook offers. There is no route to PST, no route to MBOX and no route to a folder of individual messages from inside the application.

The archive lands wherever you chose to save it, so there is no fixed OLM location. The live profile is a separate thing and worth backing up alongside the archive. It sits in a hidden folder inside your Library. The exact path is here, along with what is inside it.

Take the whole folder if you take anything. Pulling the individual message files out on their own gets you nothing usable.

Check the archive before you trust it

An OLM holds mail, folder structure, attachments, contacts, calendar entries and notes. Two things are not in it at all, so note them down separately before you switch. Signatures and client side rules are application settings rather than mailbox content. No export carries them.

Check the folder counts you wrote down in step two against what the archive actually contains. A grand total that matches can still conceal one absent subfolder. That is the failure which survives longest without being spotted. A mailbox holding 41,600 messages that exports 41,000 looks close enough at a glance.

Three checks are worth the ten minutes they take.

• Folder by folder, not in total. Compare counts per folder rather than one number for the mailbox.
• Open the oldest thing in there. Corruption and truncation show up at the far end of an archive rather than the near end. That is the part written last.
• Open an attachment. A message that lists a file but cannot produce it has not really travelled. Some export routes fold the contents into the message text and leave the listing behind.

A file size that looks plausible proves nothing. An export that stopped at 60 per cent still produces a valid OLM. The file still opens.

If you have already switched to the new Outlook for Mac

Going back is possible on most licences while legacy still runs. In Office for Mac 16.58 and later the route is Help then Revert to Legacy Outlook rather than a toggle in the main window. The local folders reappear along with the Export option, so you can run the export and then switch forward again.

Some licences have no way back. Microsoft removed the revert option entirely from Office 2024 Home and Business for Mac, by design. If your organisation sets admin preferences for Outlook, those can also pin you to one client or hide the switch. In either case the export has to happen from a machine that still runs legacy.

If no such machine exists, you have not lost everything. Server mail is still reachable through Outlook on the web, through the new client and through any IMAP client you point at the account. Only the On My Computer folders are stranded. Those sit inside the old profile folder, which a Time Machine backup will hold if one was running. Restoring that folder onto a Mac with legacy Outlook installed puts the export back within reach.

That route closes in October for Exchange Online mailboxes. After it does, an OLM you already hold is still readable, but it needs something other than Outlook to read it. Converting the archive to MBOX, PST, EML, EMLX, MSG or PDF keeps the mail open to you whatever Microsoft does with the client. Contacts and calendars can come out as CSV, vCard and ICS at the same time. An OLM converter for Mac reads the file directly on macOS, with no Outlook installed at all.

For getting that export onto storage you control, archiving Mac email to an external drive covers the rest. For the mailbox itself rather than the local folders, a tenant level backup is the more durable answer. It takes a copy of what is on the server and puts it somewhere Microsoft does not control. That sits apart from this one and is worth solving on its own terms.

Whatever you choose, do the export first. The deadline is fixed and the export is one pass through a menu, however long the copy itself takes.