Setting different reply-to message in Python email/smtplib

Question

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@gmail.com"
   msg['To'] = to
   msg['Subject'] = subject
   msg['Reply-to'] = "email2@domain2.com"

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

Thanks.