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 message notification 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>.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_default.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
user_profile.email, when passing data into the
user_profile.emailfield may not always be valid.
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
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.
Testing in a real email client
You can also forward all the emails sent in the development
environment to an email account of your choice by clicking on
Forward emails to an email account on the
/emails page. This
feature can be used for testing how the emails gets rendered by
actual email clients. This is important because web email clients
have limited CSS functionality, autolinkify things, and otherwise
mutate the HTML email one can see previewed on
To do this sort of testing, you need to set up an outgoing SMTP provider. Our production advice for Gmail and transactional email providers are relevant; you can ignore the Gmail warning as Gmail’s rate limits are appropriate for this sort of low-volume testing.
Once you have the login credentials of the SMTP provider, since there
/etc/zulip/settings.py in development, configure it using the
following keys in
email_host- SMTP hostname.
email_port- SMTP port.
email_host_user- Username of the SMTP user
email_password- Password of the SMTP user.
email_use_tls- Set to
truefor most providers. Else, don’t set any value.
Here is an example of how
zproject/dev-secrets.conf might look if
you are using Gmail.
email_host = smtp.gmail.com
email_port = 587
email_host_user = email@example.com
email_use_tls = true
# This is different from your Gmail password if you have 2FA enabled for your Google account.
# See the configuring Gmail to send email section above for more details
email_password = gmail_password
Images won’t be displayed in a real email client unless you change the
images_base_urlused for emails to a public URL such as
https://chat.zulip.org/static/images/emails(image links to
localhost:9991aren’t allowed by modern email providers). See
zproject/email_backends.pyfor more details.
While running the backend test suite, we use
django.core.mail.backends.locmem.EmailBackendas the email backend. The
locmembackend 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.
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 generally 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
css-inline 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
.html template. The
is used directly, while
.html is processed by
css-inline, which injects
the CSS we use for styling our emails (
into the templates just before sending an email.
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). 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
manage.py makemessages and then searching
for the strings in
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
.html markup, so that we don’t
need to maintain two copies of each email’s text.