Email Rescue Guide
By A Pegasus install that will not open is usually one of four faults. It is installed under Program Files, which Windows 10 and 11 block. A corrupt .CNM file in the new-mail folder makes it freeze at Opening New Mail. A stale PMAIL.CFG stops the setup screen. Or the mailbox path no longer matches after a move. Fix those in order, and if it still stays shut, the mail is intact in C:\PMAIL and can be converted without the program.
You double-click the icon, the splash screen shows for a second and then nothing. Or it hangs at Opening New Mail and the next try says Mailbox is Locked. It feels like years of email have gone with it. They have not. The program keeps everything as plain files on disk, and a failed start does not touch them.
This guide walks through the four causes that account for almost every failed start on the PMAIL community, with the fix for each. Then it covers the other way out: reading or converting the mail files directly, so you are not stuck waiting on a program from the 1990s to cooperate.
Why Will Pegasus Mail Not Open?
Pegasus Mail, David Harris's client from 1990, was built for a Windows that let programs write wherever they were installed. Modern Windows does not, and that gap explains the most common failure. The four causes that come up again and again on the PMAIL community are these.
- It is installed under Program Files. Windows 10 and 11 refuse to let the program write there, so it shows its splash screen and quits with no error and nothing left in Task Manager. This is the single most common cause.
- A new-mail file is corrupt. Every incoming message is a separate
.CNMfile. One bad one, often 0 bytes, makes the program hang at Opening New Mail. The next attempt reports Mailbox is Locked because the first one never finished. - The configuration file is stale.
PMAIL.CFGin the program folder records the setup. When it is out of step with the machine, the program opens to nothing or the first-run screen never appears. - The mailbox path no longer matches. After a reimage, a new drive letter or a copy from another PC, the program cannot find the folder it expects and opens empty or not at all.
How Do I Fix Pegasus Mail When It Will Not Start?
Work through these in order. Each one takes a few minutes and none of them deletes your mail. Back up the C:\PMAIL\MAIL folder first if you can, then start at the top.
Check where Pegasus Mail is installed
Right-click the Pegasus Mail shortcut and choose Open file location. If the folder is anywhere under C:\Program Files or C:\Program Files (x86), that is the problem. Windows 10 and 11 stop the program writing to that area, so it flashes its splash screen and quits with no error. Uninstall it, delete that folder and reinstall to C:\PMAIL. Your mail is not in the program folder, so nothing is lost by this.
Look for a broken new-mail file
If the program hangs at Opening New Mail and later shows Mailbox is Locked, one incoming message file is corrupt. Open C:\PMAIL\MAIL\ADMIN (or your user's folder) in File Explorer, sort by size and move any .CNM file of 0 bytes to a spare folder. If there are none, move the .CNM files newer than the last good start out, launch, then put them back a few at a time to find the one that fails.
Reset the setup file if the welcome screen never appears
When the program starts but shows nothing or the first-run screen refuses to appear, the configuration file is usually the fault. Find PMAIL.CFG in the program folder and delete it. On the next launch the setup screen returns. Choose the single-user option and, on Windows 10 or 11, run that first launch as administrator once so it can write its settings.
Rebuild the registry entries after a move or a drive change
If the PC was reimaged, the drive letter changed or the mailbox came from another machine, the program may open to an empty or missing mailbox. Run winpm-32.exe -A from the C:\PMAIL\PROGRAMS folder at a command prompt. The -A switch rewrites the registry entries that tell the program where its mailbox lives. Then confirm the paths under Help > About Pegasus Mail > Info.
Make sure C:\TEMP exists
Some parts of the program, including the HTML renderer, still write scratch files to C:\TEMP. On a fresh Windows install that folder is missing. Create C:\TEMP by hand and give every user read and write access to it. It is a small thing, but on the PMAIL community it has cured more than one start-up failure.
Are My Emails Lost If Pegasus Mail Will Not Open?
No. This is the part worth saying twice. The program stores every folder as a .PMM file with a .PMI index beside it, and every unread message as its own .CNM file, all under C:\PMAIL\MAIL in a folder named after the user. The program is a viewer for those files. When the viewer breaks, the files stay where they are.
So before you spend an evening on fixes, open C:\PMAIL\MAIL in File Explorer and look. If the .PMM and .CNM files are there and the drive reads them, your mail is safe. Copy that whole folder somewhere else now, then decide whether to repair the program or skip it.
How Do I Get Emails Out Without Opening Pegasus Mail?
Sometimes the fixes do not land, you are out of time or the plan was to leave Pegasus behind anyway. In every one of those cases you can work from the files directly. Univik Pegasus Converter reads .PMM, .CNM and .PMI files on Windows with no Pegasus install at all.
- Copy the mail folder from
C:\PMAIL\MAILto somewhere safe. If the old PC will not boot, take the drive out and read it from another machine. - Load it in Univik Pegasus Converter. Point the tool at the copied folder and the whole mailbox appears with its folders in place, including the loose new-mail messages that the program itself choked on.
- Choose where it goes. Outlook PST for a local Outlook, or a direct upload into Office 365, Gmail, Thunderbird or an IMAP account. MBOX, EML, PDF, HTML and CSV cover archives and records.
The files are read and left untouched, so you can try this and still go back to repairing the program later. For a quick look at a single folder, the online Pegasus Mail viewer opens a .PMM or .CNM file in a browser with nothing installed.
Half the people who reach us with a dead Pegasus install have already tried reinstalling three times. The install was never the problem. The mail was sitting in C:\PMAIL the whole time, and that folder is all we need.
Fix Pegasus Mail or Get the Mail Out?
Both are reasonable. The table sets them side by side so you can pick without guessing.
| Question | Repair the program | Convert the files |
|---|---|---|
| You want to | Keep Pegasus Mail running | Get the mail into Outlook, Office 365 or Gmail |
| Start with | The five fixes above, in order | A copy of the PMAIL folder |
| Pegasus Mail must open | Yes, that is the goal | No, never |
| Risk to your mail | None if you only move or delete .CNM and .CFG files | None, the files are only read |
| Time | Ten minutes to an hour | About ten minutes plus any upload |
| Best when | You like Pegasus Mail and the PC is staying | You were leaving anyway, or you need the mail today |
Univik Pegasus Converter reads every .PMM, .CNM and .PMI file inside the PMAIL folder and turns the mailbox into Outlook PST, MBOX or EML. It can also send it straight into Office 365, Gmail or Thunderbird, folder tree intact. The program never has to start.
Runs on Windows 7 to 11 · files stay on your PC · the trial converts a few messages per file
The short version
- A splash screen that flashes and closes means a Program Files install. Reinstall to C:\PMAIL.
- A hang at Opening New Mail, then Mailbox is Locked, means a bad .CNM file. Remove the zero-byte one.
- No setup screen means a stale PMAIL.CFG. Delete it and run once as administrator.
- An empty mailbox after a move means the paths changed. Run winpm-32.exe -A.
- Your mail is in C:\PMAIL\MAIL either way, and Univik Pegasus Converter can open it without the program.
Open the mail without Pegasus, free trial
Pegasus Mail Start-Up Questions
About This GuideResearched and written by Leena Taylor Paul for Univik, a Windows software developer since 2013. The four causes and their fixes come from real start-up failures worked through on the PMAIL community forum, including the Program Files and zero-byte .CNM cases, and were checked against a Pegasus Mail install at C:\PMAIL. Checked 22 September 2026. Still stuck? Ask the support team, the link sits below.
Sources: PMAIL community forum · pmail.com · the Univik Pegasus Converter page