If you remain concerned about C: you have the option of copying your current Pegasus Mail installation to a USB device and running it from there with the -ROAM command line switch.   This assumes that the mailbox directories are inside of E:\PMAIL.  A couple of drawbacks are a noticeable but not crippling slowness because of read/write speed and you can't make it the default mailer.

It appears that win 10 no longer accepts virtual drives, so I transferred E:\PMAIL to C:\E-data\PMAIL

When I changed the shortcut to indicate the new location it starts up Pegasus without any trouble, but all my emails and a pageful of folders, and probably all my identities as well.

How do I tell Pegasus where to find this information again? Fortunately I haven't deleted the original so I can continue using  that, but Windows 10 Backup won't work until I can delete the virtual drives.

You will need to do a clean install of Pegasus Mail to the default location of c:\pmail and then copy data from the old mailbox directory (ies?) to the new.  The user names of the new installation must match those of the old one

so if you had multiple users create the same users in the new install. 

If the old installation used only the default user of "Admin" then you

can install the new one as a single user

There is a white paper that details which mailbox files to copy that can be downloaded from the downloads section of this site.

http://community.pmail.com/files/folders/whitepapers/entry41852.aspx

Thanks Brian,

I'll try that. I did the original setup when windows was becoming corrupt every year or two and losing all the data in drive C: so I created many virtual drives, which didn't become deleted when I re-installed Windows.

I hope that I'll eventually get windows 10 backup working and hope that that will protect me against Windows becoming corrupted again.