c# - japanese email subject encoding

Question

Aparently, encoding japanese emails is somewhat challenging, which I am slowly discovering myself. In case there are any experts (even those with limited experience will do), can I please have some guidelines as to how to do it, how to test it and how to verify it?

Bear in mind that I've never set foot anywhere near Japan, it is simply that the product I'm developing is used there, among other places.

What (I think) I know so far is following:
- Japanese emails should be encoded in ISO-2022-JP, Japanese JIS codepage 50220 or possibly SHIFT_JIS codepage 932
- Email transfer encoding should be set to Base64 for plain text and 7Bit for Html
- Email subject should be encoded separately to start with "=?ISO-2022-JP?B?" (don't know what this is supposed to mean). I've tried encoding the subject with

"=?ISO-2022-JP?B?" + Convert.ToBase64String(Encoding.Unicode.GetBytes(subject))

which basically gives the encoded string as expected but it doesn't get presented as any japanese text in an email program
- I've tested in Outlook 2003, Outlook Express and GMail

Any help would be greatly appreciated

---

Ok, so to post a short update, thanks to the two helpful answers, I've managed to get the right format and encoding. Now, Outlook gives something that resembles the correct subject:
=?iso-2022-jp?B?6 Japanese test に各々の視点で語ってもらった。 6相当の防水?=

However, the exact same email in Outlook Express gives subject like this:
=?iso-2022-jp?B?6 Japanese test 縺?蜷???隕也せ縺?隱槭▲縺?繧ゅｉ縺?縺溘? 6逶?蠖薙?髦?豌??=

Furthermore, when viewed in the Inbox view in Outlook Express, the email subject is even more weird, like this:
=?iso-2022-jp?B?6 Japanese test ??????????????? 6???????=

Gmail seems to be working in the similar fashion to Outlook, which looks correct.

I just can't get my head around this one.

Answer 1

I've been dealing with Japanese encodings for almost 20 years and so I can sympathize with your difficulties. Websites that I've worked on send hundreds of emails daily to Japanese customers so I can share with you what's worked for us.

• First of all, do not use Shift-JIS. I personally receive tons of Japanese emails and almost never are they encoded using Shift-JIS. I think an old (circa Win 98?) version of Outlook Express encoded outgoing mail using Shift-JIS, but nowadays you just don't see it.

• As you've figured out, you need to use ISO-2022-JP as your encoding for at least anything that goes in the mail header. This includes the Subject, To line, and CC line. UTF-8 will also work in most cases, but it will not work on Yahoo Japan mail, and as you can imagine, many Japanese users use Yahoo Japan mail.

• You can use UTF-8 in the body of the email, but it is recommended that you base64 encode the UTF-8 encoded Japanese text and put that in the body instead of raw UTF-8 text. However, in practice, I believe that raw UTF-8 text will work fine these days, for the body of the email.

• As I alluded to above, you need to at least test on Outlook (Exchange), Outlook Express (IMAP/POP3), and Yahoo Japan web mail. Yahoo Japan is the trickiest because I believe they use EUC for the encoding of their web pages, and so you need to follow the correct standards for your emails or they won't work (ISO-2022-JP is the standard for sending Japanese emails).

• Also, your subject line should not exceed 75 characters per line. That is, 75 characters after you've encoded in ISO-2022-JP and base64, not 75 characters before conversion. If you exceed 75 characters, you need to break your encoded subject into multiple lines, starting with "=?iso-2022-jp?B?" and ending with "?=" on each line. If you don't do this, your subject might get truncated (depending on the email reader, and also the content of your subject text). According to RFC 2047:

"An 'encoded-word' may not be more than 75 characters long, including 'charset', 'encoding', 'encoded-text', and delimiters. If it is desirable to encode more text than will fit in an 'encoded-word' of 75 characters, multiple 'encoded-word's (separated by CRLF SPACE) may be used."

• Here's some sample PHP code to encode the subject:

 // Convert Japanese subject to ISO-2022-JP (JIS is essentially ISO-2022-JP)

 $subject = mb_convert_encoding ($subject, "JIS", "SJIS");

 // Now, base64 encode the subject

 $subject = base64_encode ($subject);

 // Add the encoding markers to the subject

 $subject = "=?iso-2022-jp?B?" . $subject . "?=";

 // Now, $subject can be placed as-is into the raw mail header.

• See RFC 2047 for a complete description of how to encode your email header.