Are these your own, new messages, or is this with replies, forwards and so forth?

There are certainly settings in Thunderbird.

Tools|Options|Advanced|General→Config Editor

I have these, as shown below. The "mail.compose.wrap_to_window_width" is the most obvious contender.

Set mailnews.wraplength to 0.

https://support.mozilla.org/en-US/questions/1161310#answer-972491

Zenos said

Are these your own, new messages, or is this with replies, forwards and so forth? There are certainly settings in Thunderbird. Tools|Options|Advanced|General→Config Editor I have these, as shown below. The "mail.compose.wrap_to_window_width" is the most obvious contender.

Zenos They are my own messages and problems. Edited config.editor as your attachment but no change, messages still disappear off the screen.

sfhowes Thanks for that but still no joy.

See the attached picture for my wrap preferences. As noted in the link I posted above, mail.compose.wrap_to_window_width has been removed (if you right-click it, Reset, the value is blank and the preference disappears when you close Options). Html and plain text messages wrap to the page width on my setup.

Two other preferences should also be set to defaults: mailnews.display.disable_format_flowed_support (false) mailnews.send_plaintext_flowed (true)

You aren't by chance writing messages in an external editor and then pasting into TB? Any text-related add-ons (test by Help/Restart with Add-ons disabled)?

Thanks but still no joy. Writing e mails in thunderbird and tried just about everything. All be it a nice program I think it will be going.