I am using Python email and smtplib to send an email from Python. I am doing this via the Gmail SMTP server using my Gmail credentials. This works fine, however I would like to specify a Reply-to email address different from the from address, so that replies go to a separate address (non-Gmail.)

I have tried creating a reply to parameter like this:

   msg = MIMEMultipart()

   msg['From'] = "[email protected]"
   msg['To'] = to
   msg['Subject'] = subject
   msg['Reply-to'] = "[email protected]"

But this doesn’t work. Can’t find any info on this in the Python docs.

Thanks.

Here’s my take on it. I believe that the “Reply-To” header should be set explicitly. The likely reason is that it’s less commonly used than headers such as “Subject”, “To”, and “From”.

python
Python 2.6.6 (r266:84292, May 10 2011, 11:07:28) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> MAIL_SERVER = 'smtp.domain.com'
>>> TO_ADDRESS = '[email protected]'
>>> FROM_ADDRESS = '[email protected]'
>>> REPLY_TO_ADDRESS = '[email protected]'
>>> import smtplib
>>> import email.mime.multipart
>>> msg = email.mime.multipart.MIMEMultipart()
>>> msg['to'] = TO_ADDRESS
>>> msg['from'] = FROM_ADDRESS
>>> msg['subject'] = 'testing reply-to header'
>>> msg.add_header('reply-to', REPLY_TO_ADDRESS)
>>> server = smtplib.SMTP(MAIL_SERVER)
>>> server.sendmail(msg['from'], [msg['to']], msg.as_string())
{}

I had the same question and all I had to do to make it work was to set the header in lowercase like so:

msg['reply-to'] = "[email protected]"

For Python3 in 2021 I would recommend the following to construct the message:

from email.message import EmailMessage
from email.utils import formataddr

msg = EmailMessage()
msg['Subject'] = "Message Subject"
msg['From'] = formataddr(("Sender's Name", "[email protected]"))
msg['Reply-To'] = formataddr(("Name of Reply2", "[email protected]"))
msg['To'] = formataddr(("John Smith", "[email protected]"))
msg.set_content("""\
<html>
  <head></head>
  <body>
    <p>A simple test email</p>
  </body>
</html>
""", subtype="html")

Then to send the message I use the following for my mail server which uses StartTLS on port 587:

from smtplib import SMTP
from ssl import create_default_context as context

with SMTP('smtp.domain.com', 587) as server:
    server.starttls(context=context())
    server.login('[email protected]', password)
    server.send_message(msg)

As Jonathon Reinhart pointed out, the “To” needs to be upper case:

msg['Reply-To'] = "[email protected]"

Only this worked for me:

msg['In-Reply-To'] = "[email protected]"

Look here: [Reply to email using python 3.4] by urban 1