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

file msg.txt:
-----------------------
Content-Type: multipart/mixed;
from: me<[email protected]>
to: [email protected]
subject: 主題

Content-Type: text/plain;charset=utf-8

主題

I use the code below to send a mail:

import smtplib
s=smtplib.SMTP('smtp.abc.com')
toList = ['[email protected]']
f=open('msg.txt') #above msg in msg.txt file
msg=f.read()
f.close()
s.sendmail('[email protected]',toList,msg)

I get mail body correctly but subject is not proper,

subject: some junk characters

主題           <- body is correct.

Please suggest? Is there any way to specify the decoding to be used for the subject also, as being specified for the body. How can I get the subject decoded correctly?

Makoto
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Rakesh
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3 Answers3

36

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?=

as complement decode may made with:

from email.header import decode_header
a = decode_header("""=?utf-8?b?5Li76aGM?=""")[0]
print(a[0].decode(a[1]))

Reference: Python - email header decoding UTF-8

Sérgio
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    Note that this uses the [`email.message.Message`](https://docs.python.org/3/library/email.compat32-message.html#compat32-message) API, which was superseded by `email.message.EmailMessage` in Python 3.6. With the new API you must assign a string: `msg['Subject'] = 'unicode string'`, as [assigning Header objects is not supported](https://bugs.python.org/issue21095). In my experience as of 3.7.3 the "legacy" API works better - some encoding bugs are fixed in 3.8 – Nickolay Jun 21 '19 at 10:41
  • Thanks for head up – Sérgio Jun 21 '19 at 17:21
8

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
Jimm Chen
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AHM
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    i'll try this, meantime is there any python api to convert to above format. i.e. automatically append the characters based on required encoding – Rakesh Aug 02 '11 at 14:13
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    I'm not sure - I just remembered that part from when I was messing around with this issue a while ago. [This answer](http://stackoverflow.com/questions/5910104/python-how-to-send-utf-8-e-mail#answer-5910530) seems to suggest that it is done right if you use the MIMEMultipart class instead of MimeWriter. – AHM Aug 02 '11 at 14:27
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    you should look up here [how to generate internationalized headers](http://docs.python.org/library/email.header.html) – mata May 20 '12 at 21:39
1

In short, if you use the EmailMessage API, you should code like this:

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

Answer from @Sérgio cannot be used in the EmailMessage API, cause only string object can be assigned to EmailMessage()["Subject"], but not an email.header.Header object.

C.K.
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