"how do i reply to an email using the python imaplib and include the original message?" Code Answer

the original mime tree structure of the incoming message is as follows (using email.iterators._structure(msg)):

multipart/mixed
    text/html                (message)
    application/octet-stream (attachment 1)
    application/octet-stream (attachment 2)

replying via gmail results in the following structure:

multipart/alternative
    text/plain
    text/html

i.e. they aren't being as smart as i thought, just discarding the attachments (good) and providing text and html versions that explicitly restructure the "quoted content."

i'm beginning to think that's all i should do too, just reply with a simple message as after discarding the attachments there's not much point in keeping the original message.

still, might as well answer my original question since i've figured out how to now anyway.

first, replace all the attachments in the original message with text/plain placeholders:

import email

original = email.message_from_string( ... )

for part in original.walk():
    if (part.get('content-disposition')
        and part.get('content-disposition').startswith("attachment")):

        part.set_type("text/plain")
        part.set_payload("attachment removed: %s (%s, %d bytes)"
                         %(part.get_filename(), 
                           part.get_content_type(), 
                           len(part.get_payload(decode=true))))
        del part["content-disposition"]
        del part["content-transfer-encoding"]

then create a reply message:

from email.mime.multipart import mimemultipart
from email.mime.text import mimetext
from email.mime.message import mimemessage

new = mimemultipart("mixed")
body = mimemultipart("alternative")
body.attach( mimetext("reply body text", "plain") )
body.attach( mimetext("<html>reply body text</html>", "html") )
new.attach(body)

new["message-id"] = email.utils.make_msgid()
new["in-reply-to"] = original["message-id"]
new["references"] = original["message-id"]
new["subject"] = "re: "+original["subject"]
new["to"] = original["reply-to"] or original["from"]
new["from"] = "me@mysite.com"

then attach the original mime message object and send:

new.attach( mimemessage(original) )

s = smtplib.smtp()
s.sendmail("me@mysite.com", [new["to"]], new.as_string())
s.quit()

the resulting structure is:

multipart/mixed
    multipart/alternative
        text/plain
        text/html
    message/rfc822
        multipart/mixed
            text/html
            text/plain
            text/plain

or it's a bit simpler using django:

from django.core.mail import emailmultialternatives
from email.mime.message import mimemessage

new = emailmultialternatives("re: "+original["subject"],
                             "reply body text", 
                             "me@mysite.com", # from
                             [original["reply-to"] or original["from"]], # to
                             headers = {'reply-to': "me@mysite.com",
                                        "in-reply-to": original["message-id"],
                                        "references": original["message-id"]})
new.attach_alternative("<html>reply body text</html>", "text/html")
new.attach( mimemessage(original) ) # attach original message
new.send()

the result ends (in gmail at least) showing the original message as "---- forwarded message ----" which isn't quite what i was after, but the general idea works and i hope this answer helps someone trying to figure out how to fiddle with mime messages.

By IvBaranov on September 27 2022