Hi rokuyama.

To set up the messages encoding, you should not need to do anything in the preference editor. Just go to Options > View > Formatting and int the Fonts & Colors part click the Advanced... button. At the bottom of the opened window you will be able to set default encoding for both incoming and outgoing messages.

Michal

Hi Michal,

sorry for the late reply, and thank you for your advise. But, unfortunately, it does not work for me. Please let me explain my motivation more in details.

(1) For daily use, I want to send Japanese messages with ISO-2022-JP, that is the preferable character set for Japanese e-mails (cf. RFC 1468 and followings).

(2) When I send English messages to open source communities, I prefer US-ASCII rather than ISO-2022-JP; For Latin characters, ISO-2022-JP is compatible to ASCII, however some communities, e.g., NetBSD, moderates messages with charset=iso-2022-jp in order to filter SPAMs from Japan.

With older version of Thunderbird (at least until 38.7.2), I achieved both (1) and (2) by setting incoming/outgoing encoding to ISO-2022-JP and mail.label_ascii_only_mail_as_us_ascii to true. However, with Thunderbird 45.0.0 and 45.1.0, messages are sent with charset=iso-2022-jp even if that do not contain any Japanese characters.

Thanks, Rin

Looking in Bugzilla leaves me with the impression that the pref was done away with as Nothing should be using that charset anymore. ISO-8859-1replaces it.

Bugs https://bugzilla.mozilla.org/show_bug.cgi?id=1070986 https://bugzilla.mozilla.org/show_bug.cgi?id=1069954

So I suggest you choose another encoding choice from the options > Text encoding menu when you are composing your mail.

Hi Matt,

thank you for your comment. I tried ISO-8859-1 as incoming/outgoing encoding instead of ISO-2022-JP; I sent 3 kinds of messages:

(1) messages with plain ASCII, something like,

   "I met the Schroedinger's cat at the corner of my place!"

(2) messages with 8bit Latin characters, e.g.,

   "I met the Schrödinger's cat at the corner of my place!"

(3) messages with Japanese characters, e.g.,

   "I met the シュレディンガーの猫 at the corner of my place!"

When mail.label_ascii_only_mail_as_us_ascii is false, both (1) and (2) are sent with charset=windows-1252. But if it is true, (1) is sent with charset=us-ascii; strangely enough, mail.label_ascii_only_mail_as_us_ascii flag does work with ISO-8859-1 whereas it fails with ISO-2022-JP.

In addition, (3) is sent with charset=UTF-8, unfortunately. This violates RFC 1468, and therefore it cannot be read with some mailers that strictly follow the related RFCs.

Thanks, Rin