I copied the PMAIL folder from a WIN10 computer to a WIN11 in C/.

When starting Pmail I get a box that requests a Pegasus Mail Username.

Where can I find the Username in the WIN10 Pmail folder?

The important thing when copying from one machine to another is that the path to the program files and the mailbox directory do not get changed. At this point, the best thing to do if you can is to open Pegasus Mail on the Win10 machine then go the Help > About Pegasus Mail. Click the Info button then, in the resulting display, find and paste into a reply the following entries:

WINPMAIL.EXE directory:
Home mailbox location:
New mailbox location:

This information will allow to describe what should be done to copy it to a different machine. You should then be able to determine and share with us what you did differently that needs to be fixed.

A couple of things.

1. Is your setup Single user or Mult-user?Single User would not prompt for a User ID, since the Mail is stored in C:\PMAIL\MAILMulti-user has sub directories for each user.

In my test mult-user setup C:\PMAIL\MAIL has

<DIR> ADMIN
69 PMAIL.USR

Only 1 user setup.
PMAIL.USR has
type PMAIL.USR
; PMAIL.USR Pegasus Mail user database.
A;Admin;Mail Administrator

In my primary email it is singe user.
Its PMAIL.USR has
; PMAIL.USR Pegasus Mail user database.
A;Admin;Mail Administrator

The C:\PMAIL\MAIL has over 340 files, since it has my users mail folder in it.
Had an Admin subdirectory, but it just has the standard dummy files.
BASIC.PNC
BLACK.PML
CACHE.PM
COPYSELF.PMI
COPYSELF.PMM
DESKTOP.PM0
FOLSTATE.PM
HIERARCH.PM
JUNK.PMI
JUNK.PMM
MAIN.PMI
MAIN.PMM
NEWCACHE.PM
'PERSONAL.PM!'
PERSONAL.PMR
PMAIL.INI
SPAMBUST.DAT
STATE.PMJ
VIEWER.PM
WHITE.PML
WORDS4.DB3

So determining if you have a single or multi-user setup is first step.

2nd step. I your have your system setup as mult-user, but are only using a single user.
To avoid the prompting of user name. Add an -I Admin to command line, and that will skip prompts.
Or use the C:\PMAIL\Programs\WSSETUP.EXE

Would enter Admin or whaterver user id you use.
Believe it creates a registry entry.

Could also look at what your C:\PMAIL\Programs\PMAIL.CFG has
type C:\PMAIL\Programs\PMAIL.CFG
With mine I just got with my mult-user setup?

type PMAIL.CFG
C:\PMAIL\MAIL\~N??????????????????????????????????????????????????C:\PMAIL\MAIL\~N???????????????????????????????????????????????????????????????????????????????????????????????????????????
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
???????????????????????????????????????????????????????????????????????????????

First time I've seen that. Usually the nulls are not shown at all, but here it shows as ?
Importand the is the ~N that shows it wants to user a user name, so prompts for one.

On my single user setup. Get this for PMAIL.CFG
C:\PMAIL\MAILC:\PMAIL\MAIL (Nulls not displayed with linux cat command).

If your PMAIL.CFG doesn't match with the actual mail setup, user the PCONFIG32.EXE
to change it (with Pegasus not running).
Run it, and the on 2nd window enter C:\PMAIL\MAIL or C:\PMAIL\MAIL~N and save then try it.

Again. Do not use and editor to modify PMAIL.CFG it is not a text file, and only PCONFIG32.EXE should be used on it.

Also, best to copy everything in C:\PMAIL to and archive or a backup folder, so it can be restored if something goes wrong.

Hope that helps.

Looked at registry and found these for Pegasus with Admin setup as user

REGPegasus.reg 
[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail]

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\BaseDir]
@="C:\\PMAIL\\Programs"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Command]
@="C:\\PMAIL\\Programs\\WINPM-32.EXE"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Identity]
@="<Default>"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Mailbox]
@="C:\\PMAIL\\MAIL\\Admin"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Newmail]
@="C:\\PMAIL\\MAIL\\Admin"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Username]
@="Admin"

[HKEY_USERS\S-1-5-21-0-0-0-1000\Software\Pegasus Mail\Version]
@="0491 32"