Thunderbird 80 column fix-emails sent also need line break at 80 columns

1. if the email written by Thunderbird is in plain text format (set here: Edit-> account settings-> Composition & addressing, you shoshould uncheck compose in HTML format for all accounts ), line wrap will be automatically performed in 72 columns. Note that the line wrap here is only visible when displaying the mail content and writing the mail. When you send an email, the line wrap will disappear. In other words, the content of your email that someone else sees is still a long line of text. Therefore, the following steps are required.

2. From: http://arapulido.com/2009/12/01/enabling-line-wrapping-in-thunderbird/#comment-807
The options mentioned in this article are set in: Edit-> preferences-> advanced (General Tab)-> Configure Editor

I am a happy user of the daily build of Thunderbird 3. although it is still under development, is the best email client for Linux I 've tried so far, at least, the one that better works for me. email search & filtering is fast and reliable.
The only thing I don't like is that wrapping your emails to 72 characters when sending plain text is not straightforward. once you have selected to send your emails as plain text and have set the line wrap option to 72, there is still one more option to tweak.
Thunderbird has a "feature" that sends by default all plain text with the option format = flowed, which unwraps the email in the client explorer. to turn this feature off, you have to toggle one of the options in the chrome Editor:
To disable flowed paragraphs, enforcing line breaks as formatted in the message, set the preference:
Mailnews. display. disable_format_flowed_support true
Http://kb.mozillazine.org/Mail_content_types#Plain_text)
To disable paragraph flow when you send plain text messages, and in the plain text part of multipart messages, set the preference:
Mailnews. send_plaintext_flowed false
Http://kb.mozillazine.org/Mail_content_types#Disabling_paragraph_flow)
I put it here, in case is helpful to someone else.