Python使用"quoted-printable“传输编码和"utf-8”内容编码发送电子邮件

Question

python的email.mime倾向于使用编码base64或7bit和us-ascii。我想使用quoted-printable和utf-8，因为这对人类更容易阅读和调试。

目前，我的电子邮件看起来像

--===============6135350048414329636==
MIME-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: base64

IyEvYmluL2Jhc2gKCmZvciBpIGluIHs4Mjg4Li44N

或

--===============0756888342500148236==
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

happy face =E2=98=BA

我希望原始的电子邮件是在引用可打印的unicode，以便它更容易为人们阅读。

--===============5610730199728027971==
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="utf-8"

happy face ☺

Answer 1

简短的回答

设置content-transfer-encoding

在创建将附加到MIMEMultipart对象的MIMEText对象时，首先将content-transfer-encoding设置为值quoted-printable，然后执行set_payload。操作的顺序很重要。

from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText

# first create MIMEText, then set content-transfer-encoding, then set payload
mt = MIMEText(None, _subtype='plain')
mt.replace_header('content-transfer-encoding', 'quoted-printable')
mt.set_payload(u'happy face ☺', 'utf-8')

# create the parent email object and the MIMEMultipart extension to it
email = MIMEMultipart('mixed')
inline = MIMEMultipart('alternative')

# assemble the objects
inline.attach(mt)
email.attach(inline)

设置电子邮件charset和各种编码

cs = charset.Charset('utf-8')
cs.header_encoding = charset.QP
cs.body_encoding = charset.QP
email.set_charset(cs)

结果

这将创建一个人类可读的原始电子邮件( base64编码的文件附件除外)

>>> print(email)
--===============5610730199728027971==
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="utf-8"

happy face ☺

--===============5610730199728027971==--

--===============0985725891393820576==
Content-Type: text/x-sh
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="test.sh"

Zm9vYmFyc2RmYXNkZmtqaGFzZGZrbGhhc2ZrbGpoYXNma2xqaGFzZmtsaGZkYXNmCg==

--===============0985725891393820576==--

长长的答案

下面是一个更长的脚本，为前面的代码片段提供了更多的上下文。

此脚本将发送一个以UTF-8编码的text/plain节。为了好玩，它还会附加一个文件。这样产生的原始电子邮件将是人类可读的(文件附件除外)。

from __future__ import print_function

from email import charset    
from email.encoders import encode_base64
from email.mime.base import MIMEBase
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
import mimetypes

# create the parent email object
email = MIMEMultipart('mixed')
# set email charset and email encodings
cs_ = charset.Charset('utf-8')
cs_.header_encoding = charset.QP
cs_.body_encoding = charset.QP
email.set_charset(cs_)

# create the 'text/plain' MIMEText
# first create MIMEText, then set content-transfer-encoding, then set payload
mt = MIMEText(None, _subtype='plain')
mt.replace_header('content-transfer-encoding', 'quoted-printable')
mt.set_payload(u'happy face ☺', 'utf-8')

# assemble the parts
inline = MIMEMultipart('alternative')
inline.attach(mt)
email.attach(inline)

# for fun, attach a file to the email
my_file = '/tmp/test.sh'
mimetype, encoding = mimetypes.guess_type(my_file)
mimetype = mimetype or 'application/octet-stream'
mimetype = mimetype.split('/', 1)
attachment = MIMEBase(mimetype[0], mimetype[1])
attachment.set_payload(open(my_file, 'rb').read())
encode_base64(attachment)
attachment.add_header('Content-Disposition', 'attachment', filename=os.path.basename(my_file))
email.attach(attachment)

结果

这将创建一个人类可读的原始电子邮件( base64编码的文件附件除外)

>>> print(email)
--===============5610730199728027971==
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="utf-8"

happy face ☺

--===============5610730199728027971==--

--===============0985725891393820576==
Content-Type: text/x-sh
MIME-Version: 1.0
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="test.sh"

Zm9vYmFyc2RmYXNkZmtqaGFzZGZrbGhhc2ZrbGpoYXNma2xqaGFzZmtsaGZkYXNmCg==

--===============0985725891393820576==--

(奖励)发送电子邮件

使用smtplib，可以通过电子邮件发送电子邮件。

import smtplib

# set email address headers
email['From'] = 'me@email.com'
email['To'] = 'you@email.com'
email['Subject'] = 'hello'

# send the email
smtp_srv = smtplib.SMTP('localhost')
smtp_srv.set_debuglevel(True)
print(mesg_html, end='\n\n')
print(email.as_string(), end='\n\n')
smtp_srv.sendmail('me@email.com', 'you@email.com', email.as_string())
smtp_srv.quit()

Answer 2

在尝试更改现有消息(email.Message对象)的正文并将其编码设置为quoted-printable时，我发现这个问题花费的精力远远超出了我的预期。

import email
#... 'part' is the Message object
content = part.get_payload(decode=True)
#... Modify content
part['Content-Transfer-Encoding'] = '8bit'
part.set_payload(content, 'UTF-8')
del part['Content-Transfer-Encoding']
email.encoders.encode_quopri(part)

现在，为什么我要设置然后删除Content-Transfer-Encoding头呢？set_payload调用将设置Content-Transfer-Encoding标头，如果不存在标头，则将数据编码为Base64。否则，set_payload调用将假定调用者已经对数据进行了编码，并且不会对其进行更改(通过编码)。因此，实际上我将Content-Transfer-Encoding头设置为什么值并不重要，只是我没有将其留空。

但是为什么我需要删除头部呢？email.encoders.encode_quopri调用将只添加一个标头，因此消息将具有多个Content-Transfer-Encoding标头。

因此，对没有Content-Transfer-Encoding头的消息使用set_payload然后使用encode_quopri将导致Base64字符串的带引号的可打印表示形式，而对于具有现有Content-Transfer-Encoding头的消息将导致具有重复头的消息。使用encode_quopri然后使用set_payload可能会导致重复的报头，但不会对消息进行编码。因此，为了避免陷入the quopri module，需要添加/删除繁琐的语句。