User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0 Build ID: 20160802213348 Steps to reproduce: Reply to a format=flowed plain text email, with also my settings set to always send with format=flowed. Actual results: Quoted text is not flowed (doesn't adapt to window size) neither on the editing window when composing reply email, neither when viewed as the received message, neither when viewed as received message in other mail programs such as geary. Expected results: The quoted text should flow. I'm not exactly sure how technically that should be achieved. Apple mail, iphone mail and geary are all able to flow quoted text (that they themselves have quoted) by doing: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable ... > 1 test testtesttest test testtesttest test testtesttest test=20 > testtesttest test testtesttest test testtesttest test testtesttest=20 > test testtesttest test testtesttest test testtesttest testEND. Thunderbirds quoted text is not flowed because it encodes it like so: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit ... > 1 test testtesttest test testtesttest test testtesttest test > testtesttest test testtesttest test testtesttest test testtesttest test > testtesttest test testtesttest test testtesttest testEND.

original email

Thanks for filing this bug report. Yes, that's an old (and very annoying) issue, unfortunately didn't get any attention for a long time. The fix likely requires a core change in the code shared with other applications like Firefox, which isn't helping either. Marking as a duplicate to keep the discussion at a single place.