Bumping because no replies. Is it possible the lines are no longer available? I just would like to know. Thank you for any info.

Do you mean stripes, as in having the background color of the header alternate between white and pale blue? That is most easily done by installing a theme. One example is Classic TB 2.

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

A more complex method applies a userChrome.css file:

http://kb.mozillazine.org/Zebra_striping

https://silvercircle.github.io/software/user-chrome-thunderbird/

Thank you for responding. I must have missed the notification so I didn't see it until now. Actually, what I want instead of zebra striping would be just a line between each email header for each mailbox. I know I had them in Eudora, and I thought I had them before, in TB. If I can't have lines (like a 1 or 2 point line), I could try zebra striping, but the newest info says Mozilla will not support custom themes after v60, so I don't want to get started with one now. The help file says that the default theme has the zebra, but I've checked and I'm running the default theme and I have no stripes. Any thoughts?

Hi I have Thunderbird, same version with no theme. I do have the vertical lines between headers. Just a suggestion - could your screen settings have been changed slightly so that there is less contrast? Screen settings changed with either the buttons on the computer screen or in the monitor settings, might have been set so bright or so low contrast that the lines are there but simply not visible. Good luck, Agnes

The default theme doesn't show zebra stripes on Windows TB, but I think it does on Mac OS X.

You can have stripes in any version of TB if you apply the userChrome method, but it's also possible to have horizontal lines with the css file given here. See the attached picture for an example of this working in TB 67b2.

Thank you, this worked, by following the various links. I really appreciate your help.

Agnes-- This didn't turn out to be the problem, but I appreciate you taking the time to try to help. --Victoria