Emailing users is essential in most web applications. For most cases, you can easily use SMTP, and in those cases, Flask-Mail is perfect. In other cases, you can only use your system’s sendmail client.

The Flask-Sendmail extension provides a simple interface to your system’s sendmail client from within your Flask application and gives you ability to send messages from your views and scripts.

Source code and issue tracking are at GitHub.

Installing Flask-Sendmail

Install with pip and easy_install:

pip install Flask-Sendmail

or download the latest version from version control:

git clone https://github.com/ajford/flask-sendmail.git
cd flask-sendmail
python setup.py install

If you are using virtualenv, it is assumed that you are installing flask-mail in the same virtualenv as your Flask application(s).

Configuring Flask-Sendmail

Flask-Sendmail is configured through the standard Flask config API. These are the available options (each is explained later in the documentation):

  • MAIL_MAILER : default ‘/usr/sbin/sendmail’
  • MAIL_MAILER_FLAGS : default ‘-t’
  • MAIL_DEBUG : default app.debug
  • DEFAULT_MAIL_SENDER : default None
  • DEFAULT_MAX_EMAILS : default None
  • MAIL_FAIL_SILENTLY : default True
  • MAIL_SUPPRESS_SEND : default False

In addition the standard Flask TESTING configuration option is used by Flask-Sendmail in unit tests (see below).

Emails are managed through a Mail instance:

from flask import Flask
from flask.ext.sendmail import Mail

app = Flask(__name__)
mail = Mail(app)

Alternatively you can set up your Mail instance later at configuration time, using the init_app method:

mail = Mail()

app = Flask(__name__)

Sending messages

To send a message first create a Message instance:

from flask.ext.sendmail import Message

def index():

    msg = Message("Hello",

You can set the recipient emails immediately, or individually:

msg.recipients = ["you@example.com"]

If you have set DEFAULT_MAIL_SENDER you don’t need to set the message sender explicity, as it will use this configuration value by default:

msg = Message("Hello",

If the sender is a two-element tuple, this will be split into name and address:

msg = Message("Hello",
              sender=("Me", "me@example.com"))

assert msg.sender == "Me <me@example.com>"

The message can contain a body and/or HTML:

msg.body = "testing"
msg.html = "<b>testing</b>"

Finally, to send the message, you use the Mail instance configured with your Flask application:


If the setting MAIL_FAIL_SILENTLY is True, and the connection fails (for example, the mail server cannot be found at that hostname) then no error will be raised, although of course no emails will be sent either.

Bulk emails

While Flask-Mail supports bulk emailing, Flask-Sendmail does not yet support it. If anyone has any suggestions on achieving bulk email support, please pull a request on Github.

Flask-Sendmail does take the max_email argument in an effort to mantain drop-in compatibility


Attachments are planned for a future release.

Unit tests and suppressing emails

When you are sending messages inside of unit tests, or in a development environment, it’s useful to be able to suppress email sending.

If the setting TESTING is set to True, emails will be suppressed. Calling send() on your messages will not result in any messages being actually sent.

Alternatively outside a testing environment you can set MAIL_SUPPRESS_SEND to False. This will have the same effect.

Header injection

To prevent header injection, attempts to send a message with newlines in the subject, sender or recipient addresses will result in a BadHeaderError.


class flask_sendmail.Mail(app=None)

Opens a connection to the system’s sendmail client.


Sends message through system’s sendmail client.

Parameters:message – Mail Message instance
send_message(*args, **kwargs)

Shortcut for send(msg).

Takes same arguments as Message constructor.

class flask_sendmail.Connection(mail, max_emails=None)

Handles connection to host.

send_message(*args, **kwargs)

Shortcut for send(msg).

Takes same arguments as Message constructor.

class flask_sendmail.Message(subject, recipients=None, body=None, html=None, sender=None, cc=None, bcc=None, attachments=None, reply_to=None, charset=None)

Encapsulates an email message.

  • subject – email subject header
  • recipients – list of email addresses
  • body – plain text message
  • html – HTML message
  • sender – email sender address, or DEFAULT_MAIL_SENDER by default
  • cc – CC list
  • bcc – BCC list
  • attachments – list of Attachment instances
  • reply_to – reply-to address
  • charset – used to set MIMEText _charset

Adds another recipient to the message.

Parameters:recipient – email address.
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