Encoding mail subject (SMTP) in Python with non-ASCII characters

Question

I am using Python module MimeWriter to construct a message and smtplib to send a mail constructed message is:

file msg.txt:
--------------------         


        

Answer 1

From http://docs.python.org/library/email.header.html

from email.message import Message
from email.header import Header
msg = Message()
msg['Subject'] = Header('主題', 'utf-8')
print msg.as_string()

Subject: =?utf-8?b?5Li76aGM?=

more simple:

from email.header import Header
print Header('主題', 'utf-8').encode()

=?utf-8?b?5Li76aGM?=

Answer 2

The subject is transmitted as an SMTP header, and they are required to be ASCII-only. To support encodings in the subject you need to prefix the subject with whatever encoding you want to use. In your case, I would suggest prefix the subject with ?UTF-8?B? which means UTF-8, Base64 encoded.

In other words, I believe your subject header should more or less look like this:

Subject: =?UTF-8?B?JiMyMDAyNzsmIzM4OTg4Ow=?=

In PHP you could go about it like this:

// Convert subject to base64
$subject_base64 = base64_encode($subject);
fwrite($smtp, "Subject: =?UTF-8?B?{$subject_base64}?=\r\n");

In Python:

import base64
subject_base64 = base64.encodestring(subject).strip()
subject_line = "Subject: =?UTF-8?B?%s?=" % subject_base64