# Messages

Mailman has its own Message classes, derived from the standard `email.message.Message` class, but providing additional useful methods.

## User notifications

When Mailman needs to send a message to a user, it creates a `UserNotification` instance, and then calls the `.send()` method on this object. This method requires a mailing list instance.

    >>> from mailman.app.lifecycle import create_list
    >>> mlist = create_list('test@example.com')

The `UserNotification` constructor takes the recipient address, the sender address, an optional subject, optional body text, and optional language.

    >>> from mailman.email.message import UserNotification
    >>> msg = UserNotification(
    ...     'aperson@example.com',
    ...     'test@example.com',
    ...     'Something you need to know',
    ...     'I needed to tell you this.')
    >>> msg.send(mlist)

The message will end up in the virgin queue.

    >>> from mailman.testing.helpers import get_queue_messages
    >>> messages = get_queue_messages('virgin')
    >>> len(messages)
    1
    >>> print(messages[0].msg.as_string())
    MIME-Version: 1.0
    Content-Type: text/plain; charset="us-ascii"
    Content-Transfer-Encoding: 7bit
    Subject: Something you need to know
    From: test@example.com
    To: aperson@example.com
    Message-ID: ...
    Date: ...
    Precedence: bulk

    I needed to tell you this.

The message above got a Precedence: bulk header added by default. If the message we’re sending already has a Precedence: header, it shouldn’t be changed.

    >>> del msg['precedence']
    >>> msg['Precedence'] = 'list'
    >>> msg.send(mlist)

Again, the message will end up in the virgin queue but with the original Precedence: header.

    >>> messages = get_queue_messages('virgin')
    >>> len(messages)
    1
    >>> print(messages[0].msg['precedence'])
    list

Sometimes we want to send the message without a Precedence: header such as when we send a probe message.

    >>> del msg['precedence']
    >>> msg.send(mlist, add_precedence=False)

Again, the message will end up in the virgin queue but without the Precedence: header.

    >>> messages = get_queue_messages('virgin')
    >>> len(messages)
    1
    >>> print(messages[0].msg['precedence'])
    None

However, if the message already has a Precedence: header, setting the precedence=False argument will have no effect.

    >>> msg['Precedence'] = 'junk'
    >>> msg.send(mlist, add_precedence=False)
    >>> messages = get_queue_messages('virgin')
    >>> len(messages)
    1
    >>> print(messages[0].msg['precedence'])
    junk