Change the preference mailnews.wraplength in Config. editor. A value of 72 wraps at 72 characters, a value of 0 wraps to the window width, a value of -1 does not wrap. Tested and working in TB 60.7.2/W10.

Negative.

First, there is no "Config" menu. Answers to support questions should always start from zero and assume no prior knowledge, especially obsolete prior knowledge that no longer applies to the current version. If you mean a submenu, you must explicitly indicate this.

Second, if what you actually mean is Edit->Preferences->Advanced->Config Editor, which should always be written exactly that way in full without exception, then this is still incorrect, because "mailnews.wraplength" is indeed already set to 72.

Tested and failing in 60.6.1 (64-bit), which is what currently ships with Fedora, and is therefore not irrelevant.

Further, searching for "wrap" in about:config (and does that window title really still make any sense?) yields the following:

devtoosl.scratchpad.wrapText modified boolean true mail.wrap_long_lines default boolean true mailnews.wraplength default integer 72 plain_text.wrap_long_lines modified boolean true view_source.wrap_long_lines default boolean false

Any thoughts on those?

(Pardon duplicate, there seems to have been a double post. I received an error from the server on the first attempt to post and therefore posted again.)

Please read: http://kb.mozillazine.org/Plain_text_e-mail_%28Thunderbird%29#Completely_plain_email

Thank you.

To be extremely clear for anyone following me, try this:

Edit->Preferences->Advanced->Config Editor

Set: mailnews.send_plaintext_flowed To: false

The disconnect that drives people nuts is that they are searching all over the net for "wrap" because nobody else in the world uses the term "flowed". More permanent penalties for being clever instead of consistent.

re :because nobody else in the world uses the term "flowed". More permanent penalties for being clever instead of consistent.

Many people do not have the knowledge of all the workings behind an email and it is not expected, so you are not alone in this respect.

It is not a just Thunderbird special thing. It is used for plain text emails and is standard terminology. It also meets the standard rules set out in RFC 3676, so Thunderbird is RFC 3676 compliant. As an example, in the headers you would typically see: Content-Type: text/plain; charset=windows-1252; format=flowed

More Info: https://www.emacswiki.org/emacs/FormatFlowed

If the language appears in an RFC, that's good enough for me. However, I've been thinking about this, and I think one way to avoid these kinds of problems might be to have a "comment" or "description" field for those config entries that is also checked when people search. Searching the tooltip text might work as well. I think it's pretty reasonable to have "wrap" be a keyword for these "flow" configuration entries, because based on the (large) number of bugs and threads I found from years past, this has always been an issue, and isn't likely to go away.

I'll look for a way to formally submit that as a suggestion.

Thanks again for your help. Feel free to send me a note if I can be useful helping test changes related to these features in the future.