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A templated email generation library

Project description


2013/10/23: although functional, genemail is still in beta, and the API may change. That said, it works quite well.

genemail makes creating and sending templated email easier. The following features are built-in:

  • Automatic html-to-text conversion so that all generated emails have both a plain-text and an HTML version. Note that if the auto- conversion is not sufficient, each version can have it’s own template.
  • Automatic inlining of CSS for maximum backward compatibility with old and/or problematic email clients.
  • Automatic attachment management allows a common email template to specify default attachments; additional attachments can be added to individual emails.
  • Support for DKIM email header generation so that emails that are indeed not spam are less likely to be identified as such.
  • Support for PGP email encryption so that emails can contain sensitive information that should not be visible to the public.
  • Preview data allows templates to define sample data so that email previews can be generated with predefined data and/or dynamic data.
  • Unit of test for generated emails is made easier thanks to a sender mechanism that allows outbound emails to be trapped for analysis instead of being delivered and a unittest mixin class that provides the assertEmailEqual method that validates that the significant email headers, structure and content are the same.



$ pip install genemail

Given the following package file structure:

-- mypackage/
   `-- templates/
       `-- email/
           |-- logo.png
           |-- invite.html
           |-- invite.spec         # if missing: defaults are used
           |     Example content:
           |       attachments:
           |         - name:  logo.png
           |           value: !include-raw logo.png
           |           cid:   true
           `-- invite.text         # if missing: auto-generated from .html

Use genemail as follows:

import genemail, templatealchemy as ta

# configure a genemail manager that uses the local SMTP server
# and uses mako templates from a python package named 'mypackage'
manager = genemail.Manager(
  sender   = genemail.SmtpSender(host='localhost', port='25'),
  provider = ta.Manager(
    source   = 'pkg:mypackage:templates/email',
    renderer = 'mako'),
  modifier = genemail.DkimModifier(
    selector = '',
    key      = '/path/to/private-rsa.key',

# get an email template object
eml = manager.newEmail('invite')

# set some parameters that will be used by mako to render the
# template
eml['givenname'] = 'Joe'
eml['surname']   = 'Schmoe'

# add an ICS calendar invite
  name        = 'invite.ics',
  value       = create_invite(...),
  contentType = 'text/calendar; name=invite.ics; method=PUBLISH')

# and send the email

# the resulting email will:
#   - have two alternative formats (text/plain and text/html)
#   - have one top-level attachment (text/calendar)
#   - have one text/html related attachment (logo.png)
#   - be DKIM-signed


TODO: add docs

DKIM Signed Email

TODO: add docs

Per-Email Value Caching

When genemail renders a typical email with HTML, plain-text, subjects, and headers all being supplied by the same template, it by default evaluates the template many times with different genemail_format values and different output renderings. This can be a problem, for example, if the template calls out to dynamically generate content that should only be evaluated once per email such as a pixel tracker.

To solve this, genemail inserts a default parameter named cache which is an “auto-caching dict”. The difference between a standard dict class and the cache parameter is that the .get method will populate itself with the default value if the specified key does not exist. Furthermore, if the default value is a callable, it will first call it (with no arguments) before caching it.

The following example makes use of a makeUniqueUrl() function that can be used to track clicks in the email on a per-email basis. If it did not use the cache object, makeUniqueUrl() would be called multiple times per email.

 Please click on the link below:
 <a href="${cache.get('myCacheKey', lambda: makeUniqueUrl())}">click me!</a>

Note that this cache is a per-email-instance cache.

Encrypted Email

The genemail pgp optional feature allows you to generate encrypted outbound email. It does this using the python-gnupg package, which in turn uses the gpg external command-line program. Genemail can both encrypt and sign the emails, or only encrypt. Steps to generate encrypted email:

1. First, create a GPG-home directory with all of the necessary keys. For example:

# create the directory
$ mkdir -p /path/to/gpghome
$ chmod 700 /path/to/gpghome

# for signing, a private key is needed. generate one:
$ gpg --homedir /path/to/gpghome --gen-key

# for encryption, the public key of every recipient of encrypted
# emails is needed. do this for every recipient:
$ gpg --homedir /path/to/gpghome --import /path/to/recipient/public.key

2. Then, configure genemail to use the genemail.modifier.PgpModifier modifier. For example:

import genemail

# configure a genemail manager using the modifier
manager = genemail.Manager(
  # ...
  modifier = genemail.modifier.PgpModifier(
    sign        = '',
    gpg_options = dict(gnupghome = '/path/to/gpghome'),
  # ...

PgpModifier takes the following parameters:

  • sign: str, optional, default: null

    If specified, it is taken to be the ID or email address of the GPG key to use to sign outbound emails. In this case, either the passphrase must be empty, or you must be using a gpg-agent. The default is null, which disables signing.

  • add_key: list(str), optional, default: ‘sign-key’

    The add_key parameter specifies IDs or email addresses that should be added to the encryption list, but not to the recipient list. This is useful if a global ‘backdoor’ key is needed. It can also be set to 'sign-key' (the default) which indicates that the signing key should be added (thus the sender can decrypt the sent messages). Set this to null to disable any addition. It can also be a list of values.

  • prune_keys: bool, optional, default: true

    If truthy (the default), then the list of email addresses for whom the email is encrypted for is reduced to the set of recipients that have an exactly matching key. If too many addresses are pruned (this can happen if the gpg binary is smarter at matching an email address to a key), then this may need to be set to false – but beware, if any address cannot be resolved to a key by gpg, then the entire encryption process fails, and the email is not sent.

  • prune_recipients: bool, optional, default: false

    If truthy, then encrypted emails will only be sent to the list of addresses that were the result of a prune_keys pruning. If they are not pruned, the recipients will receive emails that they cannot read. This is by default false so that it is more obvious that some action needs to be taken (i.e. give the GPG-home directory the appropriate list of keys).

  • gpg_options: dict, optional

    This parameter is a collection of parameters passed to gnupg. The only required parameter is gnupghome, which is the path to the GPG-home directory. All currently available parameters:

    • gnupghome: str, optional, default: null
    • gpgbinary: str, optional, default: ‘gpg’
    • use_agent: bool, optional, default: false
    • verbose: bool, optional, default: false
    • keyring: str, optional, default: null
    • secret_keyring: str, optional, default: null
    • options: list(str), optional, default: null

Unit Testing

The following example test code illustrates the recommended approach to do unit testing with genemail (note the use of the pxml library to compare HTML output):

import unittest, pxml, genemail, genemail.testing

class AppTest(genemail.testing.EmailTestMixin, pxml.XmlTestMixin, unittest.TestCase):

  def setUp(self):
    super(AppTest, self).setUp()
    self.sender = genemail.DebugSender()
    # the following is very subjective to how your app is built & used,
    # but the idea is to provide a different `sender` to genemail... = App() = self.sender

  def test_email(self):

    # do something to cause an email to be sent

    # verify the sent email (which will have been trapped by self.sender)
    self.assertEqual(len(self.sender.emails), 1)
    self.assertEmailEqual(self.sender.emails[0], '''\
Content-Type: multipart/alternative; boundary="==BOUNDARY-MAIN=="
MIME-Version: 1.0
Date: Fri, 13 Feb 2009 23:31:30 -0000
Message-ID: <>
Subject: Test Subject

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

Email text version.

Content-Type: multipart/related; boundary="==BOUNDARY-HTMLREL=="
MIME-Version: 1.0

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

<html><body>Email html version.</body></html>

Content-Type: image/png
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment
Content-ID: <logo.png>


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