Good detective work :-)

Seemingly out of the blue, entries in the message list are underlined.

How can the underline be eliminated? 

UPDATE 5/18/2016

I've attached a jpeg showing what I mean. 

I don't

recall ever seeing underlined messages in the new mail folder or any other folder list so don't know of a cause. 

Have you restarted since the underlines appeared?

Is it occurring in all folders or just the new mail folder?

Have you tried changing the font then changing it back?

Yes to

- Restarted 

- All folers

-  Changed font

I uninstalled then reinstalled 4.72. That did not get rid of the underlined messages.

The facts that only the text is underlined and the underline is the same color as the text makes me think it is a font issue but I remain clueless so if I were in your situation I would test changing the message list font to match the folder list font if it isn't the same already.

Have you tried adjusting 'Tools > Options > User Interface > List displays' to see if that will remove the underlining.

I'm with Brian. Can't recall seeing this before.

A very logical suggestion. However, I tried changing fonts without success. Next I uninstalled Pegasus & reinstalled it. That didn't fix it either. Finally, I replaced the file MAIL.INI that was in the original MAIL folder with the new one created by the new install. That did fix the problem.

I'm confused.  First, I am not aware of the existence of a MAIL.INI file so assume you mean the PMAIL.INI file.  Second, a reinstall should not create a new PMAIL.INI file.  An uninstall/reinstall removes/reinstalls the program files but reuses the same mailbox directories which is where the PMAIL.INI file resides.  Regardless, I'm glad you got it fixed.  Did you compare the files to see if you could identify an entry that was causing the problem?

Also, be aware that the PMAIL.INI file contains most of the configuration settings.  This could be problematic if the new install had not been fully configured or was not configured identically to the old one.  You may want to check all of the configuration settings, by identity.

Yes, I meant PMAIL.ini.

In order to make sure I would not lose my messages I temporarily moved the MAIL folder to my desktop and renamed it MAIL. The new install created a new one MAIL folder, complete with a new PMAIL.ini file. Then I renamed the newly created MAIL folder to MAIL.new. At that point I was using my original PMAIL.ini file. The underline problem apparently was in that file. I then copied PMAIL.ini from the MAIL.new folder and the underline behavior was no longer an issue. 

Yes, I had to set up new online accounts and check other settings. But now Pegasus is behaving as it should.

Thanks for the additional details.  It all makes sense now.  You did good, obviously!

Same problem happened again.

The cause is a corrupted  line into the Pmail.ini file which is an ascii (text) file.

The line reads something like "Font to use in folder browser             = Arial, 20, -8769"

Correct to "Font to use in folder browser             = Arial, 20, 0 (or 1 or 2 or 3)"

and that's it. 

20 means font size, 0 plain text, 1 bold, 2 italic, and 3 bold + Italic