Mail Send-receive In Google App Engine (reply_to Field)

I am reading about mail send/receive in GAE and I have a question about how to use reply_to and the form of the email address replied to. My register.py simply writes message.sende

Solution 1:

The reply_to address should be a canonical email address without the /_ah/mail/ prefix and it follows the same restriction of the sender mail address.

The sender address of a message must be the email address of an administrator for the application, the Google Account email address of the current user who is signed in, or any valid email receiving address for the app.

To test it on your dev server, you could configure sendmail and send a mail from your program. Once received, clicking reply from your mail client should show the reply_to mail address set in your code.

Solution 2:

mail.send_mail(sender="<az@example.com>",
           to=message.sender,
           body="reply to this email to register"
           reply_to="register@hello-1-world.appspotmail.com")