Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. An OLM is a Mac Outlook export, and Microsoft 365 cannot read it directly, so you move the mail up into the cloud mailbox. With Mac Outlook you can import the OLM and drag it into your 365 account for free. A converter uploads OLM straight to Office 365 without Mac Outlook, in bulk.
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Why OLM does not load into Microsoft 365 directly?
An OLM file is what Outlook for Mac exports, and it holds your whole Mac mailbox, emails, attachments, calendars and contacts, in one file. Microsoft 365 is a cloud mailbox on the other side, and it has no button that reads an OLM. So uploading OLM files to an Office 365 account is really about moving the mail up into the cloud, not opening a file. There are two honest ways to do that, one free through Mac Outlook and one direct with a converter, and which fits depends on what you have and how much mail is involved.
OLM reaches Microsoft 365 through Mac Outlook or a converter, never on its own.
Which way fits you?
If you still have Outlook for Mac, you can do this for free by importing the OLM and dragging it into your 365 account, which then syncs to the cloud. If you do not have Mac Outlook, or you have several OLM files or a large mailbox, a converter uploads the OLM straight into Office 365 on its own. Here is how the two compare.
Mac Outlook drags mail up for free. A converter uploads OLM to 365 without it, in bulk.
Upload OLM to Office 365 free with Mac Outlook
If Outlook for Mac is available, this costs nothing and avoids the roundabout Gmail tricks some older guides suggest.
Step 1. In Outlook for Mac, go to File then Import, choose Outlook for Mac archive file (.olm), and import your OLM. It lands under On My Computer.
Step 2. Add your Microsoft 365 account in Outlook for Mac if it is not there already, and let it connect.
Step 3. Drag the imported folders from On My Computer into your Microsoft 365 mailbox in the sidebar.
Step 4. Outlook uploads the dragged mail to the 365 server. Leave it to finish, and the emails appear in your account online.
It is free and keeps everything inside Outlook, but it does need Mac Outlook, and a large mailbox can take a long time to sync up and occasionally stalls partway. If that is not for you, the converter below skips Mac Outlook completely.
Upload OLM to Office 365 directly with a converter
A converter reads the OLM file and uploads it straight into a Microsoft 365 mailbox, with no Mac Outlook in the middle. The PCDOTS OLM Converter loads one or many OLM files, connects to your 365 account, and transfers the mail in one run while keeping folders and attachments in place. A free demo moves a limited number of items per folder so you can test it on your own data, and the full version lifts that limit.
Uploading OLM files straight into a Microsoft 365 mailbox without Mac Outlook.
Here are the steps with the screens.
Step 1. Run the converter, open the menu, go to Email Data Files and select your OLM files, then upload them.
Step 2. Preview the mailbox and select the emails or folders you want to upload.
Step 3. Open the Export menu and choose Office 365 as the destination.
Step 4. Enter your Office 365 login, click Add, and the upload starts. Watch it finish on screen.
“The old habit of bouncing an OLM through a Gmail label to reach 365 is where data goes missing, folders flatten and dates drift. A direct path is cleaner, whether that is dragging inside Mac Outlook or a converter that writes to the mailbox over the 365 connection. Either way, keep the folder tree intact and the migration stays trustworthy.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
Keeping folders and attachments
Whichever route you use, the aim is that your 365 mailbox looks like your old Mac one. A clean upload preserves the folder tree, so Inbox, Sent and your custom folders arrive separately rather than merged, and it keeps attachments inside each message. For a large migration this is what makes the result usable, since a flattened pile of thousands of emails is far harder to work with. If you would rather land the mail as a file first, you can also convert OLM to PST and then import that PST to Office 365.
The two methods compared
When the free route is enough, and when a converter is the better call.
| Method | Best for | Good to know |
|---|---|---|
| Mac Outlook drag | Having Mac Outlook, smaller mailboxes | Free, slow to sync large data |
| OLM Converter | No Mac Outlook, bulk, filters | Free demo, paid full version |
| OLM alone | Nothing, 365 cannot read it | You must use one of the above |
Frequently asked questions
How do I upload OLM files to an Office 365 account?
Import the OLM into Outlook for Mac and drag the folders into your Microsoft 365 mailbox to sync them up for free, or use a converter to upload the OLM straight into 365 without Mac Outlook.
Can I import OLM to Office 365 without Outlook?
Yes. A converter connects to your Microsoft 365 account and uploads the OLM directly, so no Outlook for Mac or Windows is needed.
Can I upload OLM to Office 365 for free?
Yes, if you have Outlook for Mac. Import the OLM, add your 365 account, and drag the mail into it so it uploads to the cloud. Only the converter route has a paid full version.
Does the upload keep folders and attachments?
A clean upload preserves the folder structure and keeps attachments inside each message, so your 365 mailbox mirrors the original Mac mailbox.
Why not route OLM through Gmail to reach 365?
That extra hop is slow and can lose data or flatten folders. A direct drag in Mac Outlook or a converter that writes to 365 is cleaner and safer.
How do I upload many OLM files at once?
A converter loads several OLM files together and uploads them to Office 365 in one run, which is much faster than dragging each mailbox by hand.
Your Mac mail, live in Microsoft 365
Uploading OLM files to Office 365 comes down to moving the mail up into the cloud, and you can pick the effort that fits. With Outlook for Mac, import the OLM and drag it into your 365 account for free. Without it, or with a lot to move, let a converter upload the OLM straight into 365 and keep the folders and attachments in order. Skip the Gmail detour either way, and your old Mac mailbox ends up live in Microsoft 365.
