Since I haven't received any messages that don't wrap, I can't test the css in the cited link, but did you double-click toolkit.legacyUserProfileCustomizations.stylesheets to true in Settings/General/Config. editor, and restart TB?

Thanks for that, it partially solves the issue, now: - The messages are wrapping when opened into their own tabs. - The message pane for the same messages are still not wrapping.

As I noted, that css mod was from a very old post - is there a more up to date way of managing wrapping of all types of messages.

I do receive some emails that do wrap (in both the message pane and the message vewing tabs), just not all messages do.

I'm not aware of a css that works for all non-wrapped messages. Do the messages that don't wrap in the Message Pane look different if View/Message Body As is Plain Text?

Perhaps you could point out which css samples from the superuser page work best, as there are a few.

This one helped:

/* Avoid annoyingly long lines */ body {

   max-width: 100%;

} pre {

   max-width: 100%;
   white-space: pre-wrap;       /* CSS 3 */

}

But also, I found there was an issue with some of the HTML being sent - specifically from my work's internal helpdesk system and once we'd addressed that formatting now they all wrap correctly.