When you reply to or forward messages from some senders, the quoted text appears in one long line, wider than the window. Edit/Rewrap adds line breaks so the text appears in the window without needing a horizontal scroll bar.

I have tried composing a plain text message with a quote and no line breaks ... clicking rewrap added no linebreaks.

Hi

This only applies if you REPLY or FORWARD, and if the original received message has all the text in a very long line going off the screen.

If the text is not in a long line off the screen, you do not need to use rewrap so nothing will happen. Any text you type yourself will not need to be rewrapped.

I hope that makes sense. Agnes

Composing in Plain Text is effected by various settings in the 'about config' settings window. So you may need to check what setting you have got set up.

• Menu app icon > Options > Options > Advanced > 'General' tab
• click on 'Config Editor' button.

By default, support for flowed plain-text format is enabled. Incoming messages with the "format=flowed" attribute set are rewrapped to utilize the full width of the message window. Outgoing messages are still wrapped regularly, but the receiving e-mail client is allowed to rewrap the message for display. There are separate preferences to disable flowed message display (mailnews.display.disable_format_flowed_support) set to false by default and sending flowed e-mails (mailnews.send_plaintext_flowed) set to true by default.

You can use mailnews.wraplength to change the line length for messages you compose (defaults to 72 characters). Although, it is buggy. If I set to 72, I actually get 64. If I set to 80, I get 70. So you do sometimes need to play around with it to get a desired result. However, if you type a contiguous line of letters with no spaces, then it is detected as a single word and you do not see a line break, so the horizontal scrollbar will appear. But unless done deliberately, that is not usually a normal part of regular writing.

Note: If you set to 0 (zero), then it should wrap to the window width if mail.compose.wrap_to_window_width set to true.

mail.compose.wrap_to_window_width set as true by default will to wrap to the window width when composing a message and mail.wrap_long_lines to control the wrapping of long lines (defaults to true).

When replying in plain text, quotes may appear as a single line per paragraph. Use Edit -> Rewrap to restore wrapping for those quotes.