A few additional notes on this since there is interest in it.

When you set up your tracker (in the demo directory usually) change the
tracker's config.ini
as below. In the [mail] section, set the following three settings:

  debug = tracker.mail

to put emails into the file tracker.mail in your tracker's home
directory. It also
prevents any attempt to deliver the email. You can read the file to view
the email
that would be sent.

Note that debug mode adds two additional fields to the stored email.
The FROM: and TO: fields should duplicate the From: and To: fields in
the email. The all
caps version records the values sent into the mailer interface, the
Mixed case version
are the headers that would be sent over the network (if debug mode was
turned off) to send
the email. It allows you to compare the values to make sure things work
as intended.

Also set:

  charset = ISO-8859-1

to prevent the body of the email (saved to tracker.email) from being
encoded using base64.
This means you can read the body of the email without using mutt or
other email reader.

The setting 

  domain = localhost

should also be set. IIRC it's set automatically.

To send email from a detector you can use:

   ## put this at the top of the file
   from roundup.mailer import Mailer


      ## then in the body of your reactor function use it like:
      # we have one or more changes to a notifiable property.
      mailer = Mailer(db.config)
      subject = 'User properties changed'
      message = """the suggested message to send to the user"""
      mailer.standard_message(addresses, subject, message)

where addresses is a list of addresses taken from the database and
oldvalues
for the user whose properties are being changed.

There is one additional issue with reactors. To see if a property has
changed, you need
to compare the property value in oldvalues and in the db. For example
with a reactor
function defined like:

  def notify_on_pw_or_email_change(db, cl, nodeid, oldvalues):

    user = db.user.getnode(db.getuid())

    changed_props = []

    if oldvalues['address'] != user['address']:
        changed_props.apppend('address')

    [... check other props like password, alternate_addresses ]

    if not changed_props: return

    [... do the notification thing ]

Having to compare that values of the properties to see what has changed
is less than ideal.
However this is the correct way to do it through version 2.6.0 of
Roundup.

=====

The below can be ignored for the purpose of this issue. It addresses the
need to 
compare values of interesting properties in the reactor rather than
checking to see 
if the properties we are interested in are "in" oldvalues. Currently:

   "interesting_prop" in oldvalues

is always true even if interesting_prop wasn't changed in this
transaction.

The spec (references.txt) for reactors says olddata (usually named
oldvalues in actual code) says: 

  For a ``set()`` operation, ``olddata`` contains the names and previous
  values of properties that were changed.

oldvalues has the previous value for *all* properties of the object, not
just
changed properties. This differs from an auditor where "'propname' in
newdata" is a
useful statement. I'll open a discussion on the dev list. If this is a
mistake
(it has been this way since version 0.5.0 AFAICT) I'll open a ticket to
fix it
in the core and reference it in this issue.