Cloud Migration Guide
By To import Pegasus Mail into Office 365, take the Pegasus user folder from C:\PMAIL\MAIL, load it into a converter that understands PMM and CNM files, choose Office 365, sign in to the Microsoft 365 mailbox and run. The folders upload in place with dates and attachments kept. If you would rather have a file, make a PST and import it through Outlook's Import/Export wizard, or for a whole company hand PST files to an admin for Microsoft Purview. The IMAP copy is free but slow and folder by folder.
Your office moved to Microsoft 365 and the old mail is still on a PC running Pegasus Mail. Microsoft's own migration tools expect an Exchange server, a PST or an IMAP mailbox to pull from. Pegasus offers none of those out of the box. So the job is to turn the Pegasus folders into something Microsoft 365 will accept.
The cleanest way is to skip the middle file altogether and upload the folders straight into the mailbox, which is what the steps below cover. The PST route and the IMAP copy still have their place, and both are laid out honestly further down.
Can Pegasus Mail Go Straight into Office 365?
Not with Pegasus Mail itself. The program from David Harris keeps folders in .PMM files and new messages in .CNM files, and it knows nothing about Microsoft 365. Microsoft's side does not read those files either. What bridges the gap is a converter that understands the Pegasus format and can also talk to a Microsoft 365 mailbox.
Univik Pegasus Converter does both. It reads the mailbox files, signs in to the Office 365 account you give it and creates the folders and messages there directly. No PST is written along the way and Outlook does not need to be installed on the PC doing the work. That is the route in the four steps that follow.
How Do I Import Pegasus Mail into Office 365?
Four steps, from the Pegasus folder on disk to the mail sitting in the Microsoft 365 mailbox. Budget half an hour plus upload time.
Gather the Pegasus mailbox files
Shut Pegasus Mail and locate the mailbox. On a normal install it sits under C:\PMAIL\MAIL, one subfolder per user name, holding the .PMM folder stores, their .PMI indexes and the loose .CNM messages. Copy that user folder somewhere handy. The upload can run from any Windows PC with an internet connection, so the old machine does not need to stay in service.
Load the mailbox in Univik Pegasus Converter
Start the converter and choose Open. Browse to the copied user folder, or on the original PC pick one of the Pegasus accounts the Open menu lists. The full folder tree appears, from New Mail down to every folder you created. Untick anything you do not want sent to the cloud.
Choose Office 365 as the destination and sign in
Select Office 365 from the output list. The tool asks you to sign in to the Microsoft 365 account that should receive the mail. Use the mailbox owner's own login. The mail travels only to that mailbox and nowhere else, and the Pegasus files on disk are read, not changed.
Run the upload and check the mailbox
Start the run. Each Pegasus folder is created in the Microsoft 365 mailbox with the same name and the messages upload into it, dates and attachments intact. When it finishes, open Outlook on the web or the Outlook app and the Pegasus folders are there under the mailbox. A large mailbox takes longer, set by your upload speed, so leave it to finish.
What If I Would Rather Import a PST?
Some IT teams want a PST in hand before anything touches the tenant, either as an archive or because several users are moving at once. In that case convert the Pegasus mailbox to PST first, then bring the PST into Microsoft 365 with Microsoft's own tools.
For one user, Outlook does it. Classic Outlook has it under File > Open & Export > Import/Export: pick Import from another program or file, then Outlook Data File (.pst), choose the PST and the mailbox folder to import into, and keep Include subfolders ticked. In new Outlook go to Settings > Data files > Import and follow the Outlook Data File (.pst) prompts, which Microsoft says need a Microsoft 365 subscription. For a whole company, an administrator can use Microsoft Purview's network upload, which takes a batch of PST files plus a mapping file that says which mailbox each one belongs to.
Is the IMAP Copy to Office 365 Worth It?
It can be, for a small mailbox. Add the Microsoft 365 account to Pegasus Mail as an IMAP account, then drag or copy each Pegasus folder into it. Pegasus pushes the messages up and they appear in the cloud mailbox. Nothing to buy, nothing to install.
The trade-offs are the same ones people hit every time. It is folder by folder, so a big mailbox is a long evening. Nested folders often come out flattened or renamed. Some servers stamp today's date on copied messages. And it only works while Pegasus Mail still opens on that PC, which on an old Windows install is not a safe bet. Fine for a dozen folders, painful for a career's worth of mail.
Most Pegasus users we hear from are one person in an office that already moved to Microsoft 365. They do not want a PST to look after, they want their folders to show up in Outlook on the web. That is why the direct upload exists.
Pegasus Mail to Office 365: Which Route?
All three end with the mail in Microsoft 365. Here is where they differ.
| Question | Direct upload | PST, then Outlook import | IMAP copy |
|---|---|---|---|
| Steps | Copy folder, sign in, run | Copy folder, make PST, import in Outlook | Set up IMAP in both apps, copy each folder |
| Middle file | None | A PST on disk | None |
| Keeps folders | Yes | Yes, with Include subfolders | Often flattened by the server |
| Works if Pegasus will not start | Yes | Yes | No |
| Needs Outlook on the PC | No | Yes, for the import | Outlook or the web app |
| Good for many users | One mailbox at a time | Yes, through Purview for admins | No |
| Cost | Free trial, then a licence | Free trial, then a licence | Free |
Univik Pegasus Converter opens your PMM, CNM and PMI files, signs in to your Office 365 mailbox and uploads the folders in place. It also writes PST, MBOX and EML. It can send to Gmail or any IMAP account instead.
Windows 7 to 11 · mail goes only to the mailbox you sign in to · the trial sends a small sample from each folder
The short version
- Pegasus Mail cannot talk to Microsoft 365, so a converter has to read its PMM and CNM files.
- Direct upload: open the user folder in Univik Pegasus Converter, choose Office 365, sign in, run. No PST needed.
- PST route: convert to PST, then import in classic Outlook through Import/Export or in new Outlook through Settings, Data files.
- Many users at once: an admin can feed PST files to Microsoft Purview with a mapping file.
- IMAP copy is free but folder by folder and needs Pegasus Mail to still open.
Upload Pegasus Mail to Office 365, free trial
Pegasus Mail to Office 365 Questions
About This GuideLeena Taylor Paul wrote this guide for Univik, maker of Windows email and file tools since 2013. The Outlook import paths and the Microsoft Purview option were checked against Microsoft's support and Learn pages in September 2026, and the converter's Office 365 output was run against a Pegasus install with configured IMAP and POP3 accounts. Checked 22 September 2026. Migrating a whole office? Talk to support through the link below.
Sources: Microsoft: import from an Outlook .pst file · Microsoft Learn: importing PST files to Microsoft 365 · Univik Pegasus Converter