This page has developer documentation on the Zulip email system. If you’re trying to configure your server to send email, you might be looking for our guide to sending outgoing email. If you’re trying to configure an email integration to receive incoming email (e.g. so that users can reply to missed message emails via email), you might be interested in our instructions for setting up an email integration.
On to the documentation. Zulip’s email system is fairly straightforward, with only a few things you need to know to get started.
- All email templates are in
templates/zerver/emails/. Each email has three template files:
<template_prefix>.source.html. Email templates, along with all other templates in the
templates/directory, are Jinja2 templates.
- Most of the CSS and HTML layout for emails is in
email_base.html. Note that email has to ship with all of its CSS and HTML, so nothing in
static/is useful for an email. If you’re adding new CSS or HTML for an email, there’s a decent chance it should go in
- All email is eventually sent by
zerver.lib.send_email.send_email. There are several other functions in
zerver.lib.send_email, but all of them eventually call the
send_emailfunction. The most interesting one is
ScheduledEmailentries are eventually processed by a supervisor job that runs
- A good way to find a bunch of example email pathways is to
One slightly complicated decision you may have to make when adding an email is figuring out how to schedule it. There are 3 ways to schedule email.
- Send it immediately, in the current Django process, e.g. by calling
send_emaildirectly. An example of this is the
- Add it to a queue. An example is the
- Send it (approximately) at a specified time in the future, using
send_future_email. An example is the
Email takes about a quarter second per email to process and send. Generally speaking, if you’re sending just one email, doing it in the current process is fine. If you’re sending emails in a loop, you probably want to send it from a queue. Documentation on our queueing system is available here.
Development and testing¶
All the emails sent in the development environment can be accessed by
/emails in the browser. The way that this works is that
we’ve set the email backend (aka what happens when you call the email
.send() method in Django) in the development environment to be our
our custom backend,
EmailLogBackEnd. It does the following:
- Logs any sent emails to
var/log/email_content.log. This log is displayed by the
/emailsendpoint (e.g. http://zulip.zulipdev.com:9991/emails).
- Print a friendly message on console advertising
/emailsto make this nice and discoverable.
You can also forward all the emails sent in the development environment
to an email id of your choice by clicking on Forward emails to a mail
/emails page. This feature can be used for testing how
emails gets rendered by different email clients. Before enabling this
you have to first configure the following SMTP settings.
- The hostname
- The username
- The password
See this section for instructions on obtaining SMTP details.
Note: The base_image_uri of the images in forwarded emails would be replaced
https://chat.zulip.org/static/images/emails inorder for the email clients
to render the images. See
zproject/email_backends.py for more details.
While running the backend test suite, we use
django.core.mail.backends.locmem.EmailBackend as the email
locmem backend stores messages in a special attribute
of the django.core.mail module, “outbox”. The outbox attribute is
created when the first message is sent. It’s a list with an
EmailMessage instance for each message that would be sent.
- After changing any HTML email or
email_base.html, you need to run
tools/inline-email-cssfor the changes to be reflected in the dev environment. The script generates files like
Zulip’s email templates live under
templates are a messy problem, because on the one hand, you want nice,
readable markup and styling, but on the other, email clients have very
limited CSS support and generaly require us to inject any CSS we’re
using in the emails into the email as inline styles. And then you
also need both plain-text and HTML emails. We solve these problems
using a combination of the
premailer library and having
two copies of each email (plain-text and HTML).
So for each email, there are two source templates: the
(for plain-text format) as well as a
.source.html template. The
.txt version is used directly; while the
.source.html template is
tools/inline-email-css (generating a
templates/zerver/emails/compiled); that tool (powered by
premailer) injects the CSS we use for styling our emails
templates/zerver/emails/email.css) into the templates inline.
What this means is that when you’re editing emails, you need to run
tools/inline-email-css after making changes to see the changes
take effect. Our tooling automatically runs this as part of
tools/provision and production deployments; but you should bump
PROVISION_VERSION when making changes to emails that change test
behavior, or other developers will get test failures until they
While this model is great for the markup side, it isn’t ideal for translations. The Django translation system works with exact strings, and having different new markup can require translators to re-translate strings, which can result in problems like needing 2 copies of each string (one for plain-text, one for HTML) and/or needing to re-translate a bunch of strings after making a CSS tweak. Re-translating these strings is relatively easy in Transifex, but annoying.
So when writing email templates, we try to translate individual sentences that are shared between the plain-text and HTML content rather than larger blocks that might contain markup; this allows translators to not have to deal with multiple versions of each string in our emails.
One can test whether you did the translating part right by running
tools/inline-email-css && manage.py makemessages and then searching
for the strings in
static/locale/en/LC_MESSAGES/django.po; if there
are multiple copies or they contain CSS colors, you did it wrong.
A final note for translating emails is that strings that are sent to user accounts (where we know the user’s language) are higher-priority to translate than things sent to an email address (where we don’t). E.g. for password reset emails, it makes sense for the code path for people with an actual account can be tagged for translation, while the code path for the “you don’t have an account email” might not be, since we might not know what language to use in the second case.
Future work in this space could be to actually generate the plain-text
versions of emails from the
.source.html markup, so that we don’t
need to maintain two copies of each email’s text.