Email Conversion Guide
By To convert Pegasus Mail to MBOX or EML, copy the user folder under C:\PMAIL\MAIL with its PMM, PMI, CNM and PMF files, open that folder in Univik Pegasus Converter, choose MBOX for one file per folder or EML for one file per message, pick an output folder and run. The folder tree is kept and attachments travel inside each message as MIME parts. Then count the From lines in an MBOX, or the .eml files in a sub-folder, against the number Pegasus showed. Pegasus itself has no MBOX or EML export, and a PMM file renamed to .mbox does not work because Pegasus separates messages with Ctrl-Z rather than a From line.
MBOX and EML are the two formats that every mail program of the last thirty years can read in some way. That is the reason to convert Pegasus Mail into them rather than into any one program's own format: the result stays useful whatever you switch to next. A Pegasus user moving to a Mac, a system administrator archiving a departed colleague's mailbox and an investigator who needs individual messages all end up here.
The complication is that Pegasus was designed in 1990 with its own storage scheme, and that scheme is close enough to MBOX to tempt people into renaming files, and far enough away that renaming fails. So the first section is about what is on the disk.
What Do the PMM, PMI and CNM Files Contain?
Open C:\PMAIL\MAIL and then the folder named after the user, and you find four kinds of file. A .PMM file is one mail folder: every message in it, one after another, in a single file, with a Ctrl-Z byte marking where one message ends and the next begins. Beside each PMM sits a .PMI file, the index. Its first 128 bytes hold the folder's display name and its ID, and the rest records where each message starts inside the PMM. Pegasus names these pairs with generated names like FOL0A3F2.PMM, which is why the index matters: without it you cannot tell Inbox from Clients.
A .CNM file is different. It is a single unread message sitting in the New Mail folder with headers and body together. Pegasus treats the New Mail folder as nothing more than a view over whatever CNM files exist. When you read a message and file it, the CNM is folded into a PMM and deleted. The fourth kind, .PMF, is an attachment from mail that arrived in Pegasus's older non-MIME form. Those files sit loose in the main directory and stay there even when the message is moved to a folder. Modern MIME mail keeps attachments inside the message, so a mailbox from the last fifteen years may have no PMF files at all.
MBOX also puts a folder's messages in one file, which is the resemblance. The difference is the separator. MBOX begins each message with a line starting From followed by a space, and readers split on that. Pegasus uses Ctrl-Z. A PMM renamed to .mbox therefore loads as a single giant message, or not at all. EML is simpler still: one message per file, headers first, which is roughly what a CNM already is.
How Do I Convert a Pegasus Mailbox to MBOX or EML?
Five steps. The conversion itself takes minutes. Most of the time goes on copying the folder and checking the result.
Gather the PMM, PMI and CNM files
Shut Pegasus down, then copy the whole user folder from C:\PMAIL\MAIL to the PC that will do the conversion. Take everything in it, not only the .PMM files: the .PMI indexes carry the folder names, the .CNM files are the unread messages and any .PMF files are attachments from older non-MIME mail. Leave out nothing and the converter can rebuild the mailbox as it was.
Open the user folder in Univik Pegasus Converter
Start the software, click Open and point it at the copied folder. The converter reads the .PMI files to recover the display name of each folder, so you see Inbox, Sent, Clients and so on rather than FOL0A3F2.PMM. Click a folder to preview its messages before deciding what to convert. On a PC where Pegasus is still installed you can pick the account from the Open menu instead.
Decide between MBOX and EML
Choose MBOX when the destination is a mail program: Apple Mail, Thunderbird, Evolution or a hosted service that imports mailboxes. Choose EML when you want messages as individual files you can search in Explorer, drag into Outlook one at a time, attach to a ticket or hand to a forensic tool. The section below the steps goes through the trade-offs in more detail.
Pick the output folder and run the conversion
Browse to an empty folder and start the run. With MBOX the output is a single .mbox for each Pegasus folder, carrying that folder's name. With EML you get a sub-folder per Pegasus folder holding one .eml per message, each named from sender, subject and date. Nested Pegasus folders become nested output folders. Attachments are carried inside each message as MIME parts, the way any modern mail program expects them.
Check the message counts
Open one of the MBOX files in a text editor and count the lines that start with From , or count the .eml files in a sub-folder in Explorer. The number should match the message count Pegasus displayed for that folder. If it comes up short, the usual cause is a folder whose .PMI index was damaged. Reindex it in Pegasus if Pegasus still runs, or convert that folder on its own and compare again.
MBOX or EML: Which One Do You Need?
Pick by what happens next, not by which sounds more standard. MBOX is a mailbox: one file holds a whole folder in order. Mail programs import it as a folder. If the Pegasus mail is heading into Apple Mail, Thunderbird, Evolution, KMail or a hosted service with a mailbox import, MBOX is the natural fit and you move one file per folder. It is also compact to store and easy to zip.
EML is a message: one file each, with headers and body and attachments inside. Windows shows EML files with a preview, Outlook opens one on double-click and lets you drag it into a folder, support systems accept it as an attachment and forensic tools ingest it directly. If the mail is going to be searched, filed, quoted or examined message by message, EML is easier to live with. When the answer is both, run the conversion twice into two folders. Loading the mailbox is the slow part and it only happens once.
The most common mistake we see with Pegasus is someone renaming a PMM to .mbox, watching Thunderbird show one message of eighty thousand lines, and deciding the folder is corrupt. It is fine. The separators are different, that is all. The PMI beside it still knows where every message starts.
How Does the MBOX Get into Apple Mail or Linux?
Copy the .mbox files to the Mac, open Mail and choose File > Import Mailboxes. Select Files in mbox format, browse to the folder that holds the files and click Continue. Apple's guide notes that the messages land in a new mailbox called Import in the sidebar, from which you drag folders and messages to where you want them and then delete the Import mailbox.
On Linux, Evolution imports MBOX from File > Import with the Berkeley Mailbox option, and Thunderbird on any platform uses the ImportExportTools NG add-on, which the Thunderbird guide covers step by step. For a web service, look for an MBOX or mailbox import in its migration settings. If there is none, the IMAP route of adding the account to Thunderbird and dragging folders up works everywhere.
MBOX, EML or the Pegasus Text Export?
Pegasus does have one export of its own: select messages, right-click and export to a text file. It is worth knowing what it gives you next to the two real formats.
| Question | MBOX | EML | Pegasus text export |
|---|---|---|---|
| Files produced | One .mbox per folder | One .eml per message | One .txt per selection |
| Opens in | Apple Mail, Thunderbird, Evolution, webmail imports | Outlook, Thunderbird, Windows preview, forensic tools | Notepad |
| Folder tree | Kept in file names | Kept as sub-folders | Lost |
| Attachments | Inside each message as MIME | Inside each message as MIME | Dropped |
| Searchable in Explorer | No, one big file | Yes, per message | Partly |
| Made by | Univik Pegasus Converter | Univik Pegasus Converter | Pegasus, right-click export |
| Needs Pegasus running | No | No | Yes |
Univik Pegasus Converter reads PMM, PMI, CNM and PMF files without Pegasus installed and writes MBOX, EML, PST, PDF, HTML or CSV with the folder tree intact. Load the mailbox once, save it in as many formats as you need.
64-bit Windows 10 and 11 · nothing uploaded · the trial writes a sample from every folder
The short version
- PMM is a folder with Ctrl-Z between messages, PMI is its index and name, CNM is one unread message, PMF is an old-style attachment.
- Renaming a PMM to .mbox fails because MBOX splits on From lines, not Ctrl-Z.
- Copy the whole user folder, open it in Univik Pegasus Converter, choose MBOX for mail programs or EML for message-by-message work, run.
- Count the From lines or the .eml files against the Pegasus folder count before you delete anything.
- Apple Mail imports the result via File, Import Mailboxes, Files in mbox format.
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Format Questions
About This GuideLeena Taylor Paul researched and wrote this for Univik, maker of Windows email converters since 2013. The file descriptions come from the Pegasus Mail file reference maintained by the Pegasus community and were confirmed by opening PMM, PMI and CNM files from a working C:\PMAIL install in a hex editor. The Apple Mail import path is taken from Apple's current Mail user guide. 22 September 2026. Count not matching? Support can look at the PMI with you.
Sources: Pegasus Mail filenames and file extensions reference · Apple Support: import or export mailboxes in Mail · Univik Pegasus Converter