Bounces

An important feature of Mailman is automatic bounce processing.

Bounces, or message rejection

Mailman can bounce messages back to the original sender. This is essentially equivalent to rejecting the message with notification. Mailing lists can bounce a message with an optional error message.

>>> mlist = create_list('ant@example.com')

Any message can be bounced.

>>> msg = message_from_string("""\
... To: ant@example.com
... From: aperson@example.com
... Subject: Something important
...
... I sometimes say something important.
... """)

Bounce a message by passing in the original message, and an optional error message. The bounced message ends up in the virgin queue, awaiting sending to the original message author.

>>> from mailman.app.bounces import bounce_message
>>> bounce_message(mlist, msg)
>>> from mailman.testing.helpers import get_queue_messages
>>> items = get_queue_messages('virgin')
>>> len(items)
1
>>> print(items[0].msg.as_string())
Subject: Something important
From: ant-owner@example.com
To: aperson@example.com
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="..."
Message-ID: ...
Date: ...
Precedence: bulk

--...
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

[No bounce details are available]
--...
Content-Type: message/rfc822
MIME-Version: 1.0

To: ant@example.com
From: aperson@example.com
Subject: Something important

I sometimes say something important.

--...--

An error message can be given when the message is bounced, and this will be included in the payload of the text/plain part. The error message must be passed in as an instance of a RejectMessage exception.

>>> from mailman.interfaces.pipeline import RejectMessage
>>> error = RejectMessage("This wasn't very important after all.")
>>> bounce_message(mlist, msg, error)
>>> items = get_queue_messages('virgin', expected_count=1)
>>> print(items[0].msg.as_string())
Subject: Something important
From: ant-owner@example.com
To: aperson@example.com
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="..."
Message-ID: ...
Date: ...
Precedence: bulk

--...
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This wasn't very important after all.
--...
Content-Type: message/rfc822
MIME-Version: 1.0

To: ant@example.com
From: aperson@example.com
Subject: Something important

I sometimes say something important.

--...--

The RejectMessage exception can also include a set of reasons, which will be interpolated into the message using the {reasons} placeholder.

>>> error = RejectMessage("""This message is rejected because:
...
... $reasons
... """, [
...     'I am not happy',
...     'You are not happy',
...     'We are not happy'])
>>> bounce_message(mlist, msg, error)
>>> items = get_queue_messages('virgin', expected_count=1)
>>> print(items[0].msg.as_string())
Subject: Something important
From: ant-owner@example.com
To: aperson@example.com
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="..."
Message-ID: ...
Date: ...
Precedence: bulk

--...
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit

This message is rejected because:

I am not happy
You are not happy
We are not happy

--...
Content-Type: message/rfc822
MIME-Version: 1.0

To: ant@example.com
From: aperson@example.com
Subject: Something important

I sometimes say something important.

--...