The Flask Mega-Tutorial Part X: Email Support

This is the tenth installment of the Flask Mega-Tutorial series, in which I'm going to tell you how your application can send emails to your users, and how to build a password recovery feature on top of the email support.

For your reference, below is a list of the articles in this series.

Note 1: If you are looking for the legacy version of this tutorial, it's here.

Note 2: If you would like to support my work on this blog, or just don't have patience to wait for weekly articles, I am offering the complete version of this tutorial packaged as an ebook or a set of videos. For more information, visit courses.miguelgrinberg.com.

The application is doing pretty well on the database front now, so in this chapter I want to depart from that topic and add another important piece that most web applications need, which is the sending of emails.

Why does an application need to email its users? There are many reasons, but one common one is to solve authentication related problems. In this chapter I'm going to add a password reset feature for users that forget their password. When a user requests a password reset, the application will send an email with a specially crafted link. The user then needs to click that link to have access to a form in which to set a new password.

The GitHub links for this chapter are: Browse, Zip, Diff.

Introduction to Flask-Mail

As far as the actual sending of emails, Flask has a popular extension called Flask-Mail that can make the task very easy. As always, this extension is installed with pip:

(venv) $ pip install flask-mail

The password reset links will have a secure token in them. To generate these tokens, I'm going to use JSON Web Tokens, which also have a popular Python package:

(venv) $ pip install pyjwt

The Flask-Mail extension is configured from the app.config object. Remember when in Chapter 7 I added the email configuration for sending yourself an email whenever an error occurred in production? I did not tell you this then, but my choice of configuration variables was modeled after Flask-Mail's requirements, so there isn't really any additional work that is needed, the configuration variables are already in the application.

Like most Flask extensions, you need to create an instance right after the Flask application is created. In this case this is an object of class Mail:

app/__init__.py: Flask-Mail instance.

# ...
from flask_mail import Mail

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

If you are planning to test sending of emails you have the same two options I mentioned in Chapter 7. If you want to use an emulated email server, Python provides one that is very handy that you can start in a second terminal with the following command:

(venv) $ python -m smtpd -n -c DebuggingServer localhost:8025

To configure for this server you will need to set two environment variables:

(venv) $ export MAIL_SERVER=localhost
(venv) $ export MAIL_PORT=8025

If you prefer to have emails sent for real, you need to use a real email server. If you have one, then you just need to set the MAIL_SERVER, MAIL_PORT, MAIL_USE_TLS, MAIL_USERNAME and MAIL_PASSWORD environment variables for it. If you want a quick solution, you can use a Gmail account to send email, with the following settings:

(venv) $ export MAIL_SERVER=smtp.googlemail.com
(venv) $ export MAIL_PORT=587
(venv) $ export MAIL_USE_TLS=1
(venv) $ export MAIL_USERNAME=<your-gmail-username>
(venv) $ export MAIL_PASSWORD=<your-gmail-password>

If you are using Microsoft Windows, you need to replace export with set in each of the export statements above.

Remember that the security features in your Gmail account may prevent the application from sending emails through it unless you explicitly allow "less secure apps" access to your Gmail account. You can read about this here, and if you are concerned about the security of your account, you can create a secondary account that you configure just for testing emails, or you can enable less secure apps only temporarily to run your tests and then revert back to the more secure default.

Flask-Mail Usage

To learn how Flask-Mail works, I'll show you how to send an email from a Python shell. So fire up Python with flask shell, and then run the following commands:

>>> from flask_mail import Message
>>> from app import mail
>>> msg = Message('test subject', sender=app.config['ADMINS'][0],
... recipients=['your-email@example.com'])
>>> msg.body = 'text body'
>>> msg.html = '<h1>HTML body</h1>'
>>> mail.send(msg)

The snippet of code above will send an email to a list of email addresses that you put in the recipients argument. I put the sender as the first configured admin (I've added the ADMINS configuration variable in Chapter 7). The email will have plain text and HTML versions, so depending on how your email client is configured you may see one or the other.

So as you see, this is pretty simple. Now let's integrate emails into the application.

A Simple Email Framework

I will begin by writing a helper function that sends an email, which is basically a generic version of the shell exercise from the previous section. I will put this function in a new module called app/email.py:

app/email.py: Email sending wrapper function.

from flask_mail import Message
from app import mail

def send_email(subject, sender, recipients, text_body, html_body):
    msg = Message(subject, sender=sender, recipients=recipients)
    msg.body = text_body
    msg.html = html_body

Flask-Mail supports some features that I'm not utilizing here such as Cc and Bcc lists. Be sure to check the Flask-Mail Documentation if you are interested in those options.

Requesting a Password Reset

As I mentioned above, I want users to have the option to request their password to be reset. For this purpose I'm going to add a link in the login page:

app/templates/login.html: Password reset link in login form.

        Forgot Your Password?
        <a href="{{ url_for('reset_password_request') }}">Click to Reset It</a>

When the user clicks the link, a new web form will appear that requests the user's email address as a way to initiate the password reset process. Here is the form class:

app/forms.py: Reset password request form.

class ResetPasswordRequestForm(FlaskForm):
    email = StringField('Email', validators=[DataRequired(), Email()])
    submit = SubmitField('Request Password Reset')

And here is the corresponding HTML template:

app/templates/reset_password_request.html: Reset password request template.

{% extends "base.html" %}

{% block content %}
    <h1>Reset Password</h1>
    <form action="" method="post">
        {{ form.hidden_tag() }}
            {{ form.email.label }}<br>
            {{ form.email(size=64) }}<br>
            {% for error in form.email.errors %}
            <span style="color: red;">[{{ error }}]</span>
            {% endfor %}
        <p>{{ form.submit() }}</p>
{% endblock %}

I also need a view function to handle this form:

app/routes.py: Reset password request view function.

from app.forms import ResetPasswordRequestForm
from app.email import send_password_reset_email

@app.route('/reset_password_request', methods=['GET', 'POST'])
def reset_password_request():
    if current_user.is_authenticated:
        return redirect(url_for('index'))
    form = ResetPasswordRequestForm()
    if form.validate_on_submit():
        user = User.query.filter_by(email=form.email.data).first()
        if user:
        flash('Check your email for the instructions to reset your password')
        return redirect(url_for('login'))
    return render_template('reset_password_request.html',
                           title='Reset Password', form=form)

This view function is fairly similar to others that process a form. I start by making sure the user is not logged in. If the user is logged in, then there is no point in using the password reset functionality, so I redirect to the index page.

When the form is submitted and valid, I look up the user by the email provided by the user in the form. If I find the user, I send a password reset email. I'm using a send_password_reset_email() helper function to do this. I will show you this function below.

After the email is sent, I flash a message directing the user to look for the email for further instructions, and then redirect back to the login page. You may notice that the flashed message is displayed even if the email provided by the user is unknown. This is so that clients cannot use this form to figure out if a given user is a member or not.

Password Reset Tokens

Before I implement the send_password_reset_email() function, I need to have a way to generate a password request link. This is going to be the link that is sent to the user via email. When the link is clicked, a page where a new password can be set is presented to the user. The tricky part of this plan is to make sure that only valid reset links can be used to reset an account's password.

The links are going to be provisioned with a token, and this token will be validated before allowing the password change, as proof that the user that requested the email has access to the email address on the account. A very popular token standard for this type of process is the JSON Web Token, or JWT. The nice thing about JWTs is that they are self contained. You can send a token to a user in an email, and when the user clicks the link that feeds the token back into the application, it can be verified on its own.

How do JWTs work? Nothing better than a quick Python shell session to understand them:

>>> import jwt
>>> token = jwt.encode({'a': 'b'}, 'my-secret', algorithm='HS256')
>>> token
>>> jwt.decode(token, 'my-secret', algorithms=['HS256'])
{'a': 'b'}

The {'a': 'b'} dictionary is an example payload that is going to be written into the token. To make the token secure, a secret key needs to be provided to be used in creating a cryptographic signature. For this example I have used the string 'my-secret', but with the application I'm going to use the SECRET_KEY from the configuration. The algorithm argument specifies how the token is to be generated. The HS256 algorithm is the most widely used.

As you can see the resulting token is a long sequence of characters. But do not think that this is an encrypted token. The contents of the token, including the payload, can be decoded easily by anyone (don't believe me? Copy the above token and then enter it in the JWT debugger to see its contents). What makes the token secure is that the payload is signed. If somebody tried to forge or tamper with the payload in a token, then the signature would be invalidated, and to generate a new signature the secret key is needed. When a token is verified, the contents of the payload are decoded and returned back to the caller. If the token's signature was validated, then the payload can be trusted as authentic.

The payload that I'm going to use for the password reset tokens is going to have the format {'reset_password': user_id, 'exp': token_expiration}. The exp field is standard for JWTs and if present it indicates an expiration time for the token. If a token has a valid signature, but it is past its expiration timestamp, then it will also be considered invalid. For the password reset feature, I'm going to give these tokens 10 minutes of life.

When the user clicks on the emailed link, the token is going to be sent back to the application as part of the URL, and the first thing the view function that handles this URL will do is to verify it. If the signature is valid, then the user can be identified by the ID stored in the payload. Once the user's identity is known, the application can ask for a new password and set it on the user's account.

Since these tokens belong to users, I'm going to write the token generation and verification functions as methods in the User model:

app/models.py: Reset password token methods.

from time import time
import jwt
from app import app

class User(UserMixin, db.Model):
    # ...

    def get_reset_password_token(self, expires_in=600):
        return jwt.encode(
            {'reset_password': self.id, 'exp': time() + expires_in},
            app.config['SECRET_KEY'], algorithm='HS256').decode('utf-8')

    def verify_reset_password_token(token):
            id = jwt.decode(token, app.config['SECRET_KEY'],
        return User.query.get(id)

The get_reset_password_token() function generates a JWT token as a string. Note that the decode('utf-8') is necessary because the jwt.encode() function returns the token as a byte sequence, but in the application it is more convenient to have the token as a string.

The verify_reset_password_token() is a static method, which means that it can be invoked directly from the class. A static method is similar to a class method, with the only difference that static methods do not receive the class as a first argument. This method takes a token and attempts to decode it by invoking PyJWT's jwt.decode() function. If the token cannot be validated or is expired, an exception will be raised, and in that case I catch it to prevent the error, and then return None to the caller. If the token is valid, then the value of the reset_password key from the token's payload is the ID of the user, so I can load the user and return it.

Sending a Password Reset Email

Now that I have the tokens, I can generate the password reset emails. The send_password_reset_email() function relies on the send_email() function I wrote above.

app/email.py: Send password reset email function.

from flask import render_template
from app import app

# ...

def send_password_reset_email(user):
    token = user.get_reset_password_token()
    send_email('[Microblog] Reset Your Password',
                                         user=user, token=token),
                                         user=user, token=token))

The interesting part in this function is that the text and HTML content for the emails is generated from templates using the familiar render_template() function. The templates receive the user and the token as arguments, so that a personalized email message can be generated. Here is the text template for the reset password email:

app/templates/email/reset_password.txt: Text for password reset email.

Dear {{ user.username }},

To reset your password click on the following link:

{{ url_for('reset_password', token=token, _external=True) }}

If you have not requested a password reset simply ignore this message.


The Microblog Team

And here is the nicer HTML version of the same email:

app/templates/email/reset_password.html: HTML for password reset email.

<p>Dear {{ user.username }},</p>
    To reset your password
    <a href="{{ url_for('reset_password', token=token, _external=True) }}">
        click here
<p>Alternatively, you can paste the following link in your browser's address bar:</p>
<p>{{ url_for('reset_password', token=token, _external=True) }}</p>
<p>If you have not requested a password reset simply ignore this message.</p>
<p>The Microblog Team</p>

The reset_password route that is referenced in the url_for() call in these two email templates does not exist yet, this will be added in the next section. The _external=True argument that I included in the url_for() calls in both templates is also new. The URLs that are generated by url_for() by default are relative URLs, so for example, the url_for('user', username='susan') call would return /user/susan. This is normally sufficient for links that are generated in web pages, because the web browser takes the remaining parts of the URL from the current page. When sending a URL by email however, that context does not exist, so fully qualified URLs need to be used. When _external=True is passed as an argument, complete URLs are generated, so the previous example would return http://localhost:5000/user/susan, or the appropriate URL when the application is deployed on a domain name.

Resetting a User Password

When the user clicks on the email link, a second route associated with this feature is triggered. Here is the password request view function:

app/routes.py: Password reset view function.

from app.forms import ResetPasswordForm

@app.route('/reset_password/<token>', methods=['GET', 'POST'])
def reset_password(token):
    if current_user.is_authenticated:
        return redirect(url_for('index'))
    user = User.verify_reset_password_token(token)
    if not user:
        return redirect(url_for('index'))
    form = ResetPasswordForm()
    if form.validate_on_submit():
        flash('Your password has been reset.')
        return redirect(url_for('login'))
    return render_template('reset_password.html', form=form)

In this view function I first make sure the user is not logged in, and then I determine who the user is by invoking the token verification method in the User class. This method returns the user if the token is valid, or None if not. If the token is invalid I redirect to the home page.

If the token is valid, then I present the user with a second form, in which the new password is requested. This form is processed in a way similar to previous forms, and as a result of a valid form submission, I invoke the set_password() method of User to change the password, and then redirect to the login page, where the user can now login.

Here is the ResetPasswordForm class:

app/forms.py: Password reset form.

class ResetPasswordForm(FlaskForm):
    password = PasswordField('Password', validators=[DataRequired()])
    password2 = PasswordField(
        'Repeat Password', validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('Request Password Reset')

And here is the corresponding HTML template:

app/templates/reset_password.html: Password reset form template.

{% extends "base.html" %}

{% block content %}
    <h1>Reset Your Password</h1>
    <form action="" method="post">
        {{ form.hidden_tag() }}
            {{ form.password.label }}<br>
            {{ form.password(size=32) }}<br>
            {% for error in form.password.errors %}
            <span style="color: red;">[{{ error }}]</span>
            {% endfor %}
            {{ form.password2.label }}<br>
            {{ form.password2(size=32) }}<br>
            {% for error in form.password2.errors %}
            <span style="color: red;">[{{ error }}]</span>
            {% endfor %}
        <p>{{ form.submit() }}</p>
{% endblock %}

The password reset feature is now complete, so make sure you try it.

Asynchronous Emails

If you are using the simulated email server that Python provides you may not have noticed this, but sending an email slows the application down considerably. All the interactions that need to happen when sending an email make the task slow, it usually takes a few seconds to get an email out, and maybe more if the email server of the addressee is slow, or if there are multiple addressees.

What I really want is for the send_email() function to be asynchronous. What does that mean? It means that when this function is called, the task of sending the email is scheduled to happen in the background, freeing the send_email() to return immediately so that the application can continue running concurrently with the email being sent.

Python has support for running asynchronous tasks, actually in more than one way. The threading and multiprocessing modules can both do this. Starting a background thread for email being sent is much less resource intensive than starting a brand new process, so I'm going to go with that approach:

app/email.py: Send emails asynchronously.

from threading import Thread
# ...

def send_async_email(app, msg):
    with app.app_context():

def send_email(subject, sender, recipients, text_body, html_body):
    msg = Message(subject, sender=sender, recipients=recipients)
    msg.body = text_body
    msg.html = html_body
    Thread(target=send_async_email, args=(app, msg)).start()

The send_async_email function now runs in a background thread, invoked via the Thread() class in the last line of send_email(). With this change, the sending of the email will run in the thread, and when the process completes the thread will end and clean itself up. If you have configured a real email server, you will definitely notice a speed improvement when you press the submit button on the password reset request form.

You probably expected that only the msg argument would be sent to the thread, but as you can see in the code, I'm also sending the application instance. When working with threads there is an important design aspect of Flask that needs to be kept in mind. Flask uses contexts to avoid having to pass arguments across functions. I'm not going to go into a lot of detail on this, but know that there are two types of contexts, the application context and the request context. In most cases, these contexts are automatically managed by the framework, but when the application starts custom threads, contexts for those threads may need to be manually created.

There are many extensions that require an application context to be in place to work, because that allows them to find the Flask application instance without it being passed as an argument. The reason many extensions need to know the application instance is because they have their configuration stored in the app.config object. This is exactly the situation with Flask-Mail. The mail.send() method needs to access the configuration values for the email server, and that can only be done by knowing what the application is. The application context that is created with the with app.app_context() call makes the application instance accessible via the current_app variable from Flask.


  • #201 Joshua said 2020-05-13T22:12:06Z

    Hey Miguel thanks for the course. I am stuck here: 2020-05-14 01:03:35,827] INFO in init: Microblog startup Usage: flask shell [OPTIONS]

    Error: While importing "microblog", an ImportError was raised:

    Traceback (most recent call last): File "c:\users\dell e7240\desktop\microblog.2\env\lib\site-packages\flask\cli.py", line 240, in locate_app import(module_name) File "C:\Users\DELL E7240\Desktop\microblog.2\microblog.py", line 1, in from app import app, db File "C:\Users\DELL E7240\Desktop\microblog.2\app__init__.py", line 41, in from app import routes, models, errors File "C:\Users\DELL E7240\Desktop\microblog.2\app\routes.py", line 8, in from app.email import send_password_reset_email ImportError: cannot import name 'send_password_reset_email' from 'app.email' (C:\Users\DELL E7240\Desktop\microblog.2\app\email.py)

  • #202 Miguel Grinberg said 2020-05-14T10:09:37Z

    @Joshua: you don't seem to have a send_password_reset_email() function in app/email.py.

  • #203 Ben Gray said 2020-05-14T18:42:21Z

    I was having problems getting mail to send with the "SMTPServerDisconnected('please run connect() first" issue. It was because I was using powershell where nstead of export or set you must use e.g. $env:MAIL_PORT="587". Hope this helps someone!

    Obligatory thanks for a great tutorial.

  • #204 Alex said 2020-05-15T09:41:44Z

    Hey Miguel thanks for the course. I am trying to reset my password using the DebuggingServer but I am not getting any feedback. Instead i get the following exception on my terminal: * Debug mode: off [2020-05-15 12:32:26,252] INFO in init: Microblog startup * Running on (Press CTRL+C to quit) - - [15/May/2020 12:32:28] "GET / HTTP/1.1" 302 - - - [15/May/2020 12:32:28] "GET /login?next=%2F HTTP/1.1" 200 - - - [15/May/2020 12:32:28] "GET /login?next=%2F HTTP/1.1" 200 - - - [15/May/2020 12:32:31] "GET /reset_password_request HTTP/1.1" 200 - - - [15/May/2020 12:32:31] "GET /reset_password_request HTTP/1.1" 200 - [2020-05-15 12:32:35,177] ERROR in app: Exception on /reset_password_request [POST] Traceback (most recent call last): File "c:\users\dell e7240\desktop\microblog.2\env\lib\site-packages\flask_mail.py", line 492, in send message.send(connection) File "c:\users\dell e7240\desktop\microblog.2\env\lib\site-packages\flask_mail.py", line 427, in send connection.send(self) File "c:\users\dell e7240\desktop\microblog.2\env\lib\site-packages\flask_mail.py", line 188, in send self.host.sendmail(sanitize_address(envelope_from or message.sender), File "C:\python\lib\smtplib.py", line 856, in sendmail self.ehlo_or_helo_if_needed() File "C:\python\lib\smtplib.py", line 604, in ehlo_or_helo_if_needed if not (200 <= self.ehlo()[0] <= 299): File "C:\python\lib\smtplib.py", line 444, in ehlo self.putcmd(self.ehlo_msg, name or self.local_hostname) File "C:\python\lib\smtplib.py", line 371, in putcmd self.send(str) File "C:\python\lib\smtplib.py", line 363, in send raise SMTPServerDisconnected('please run connect() first') smtplib.SMTPServerDisconnected: please run connect() first

  • #205 Miguel Grinberg said 2020-05-15T14:11:46Z

    @Alex: check your configuration, my guess is that the app is trying to send emails through another SMTP server, not the debugging server you are running.

  • #206 ganesh said 2020-05-18T12:05:09Z

    Hey Miguel! I am trying to send mails from flask to g-mail. I am using the O'REILLY 2ND EDITION. I have set the environmental variables and executed the following code which is in the book: ---------------code--------------------- (venv) $ flask shell

    from flask_mail import Message from hello import mail msg = Message('test email', sender='you@example.com', ... recipients=['you@example.com']) msg.body = 'This is the plain text body' msg.html = 'This is the HTML body' with app.app_context(): ... mail.send(msg) ... ------------------------X--------------------------------------

    I am getting this error in the flask shell. ------------------------ERROR--------------------------- ConnectionRefusedError: [WinError 10061] No connection could be made because the target machine actively refused it ---------------------------X------------------------ Thanks in advance.

  • #207 Miguel Grinberg said 2020-05-18T16:59:38Z

    @ganesh: run the application in debug mode, and then Flask-Mail will dump a lot more information to your terminal window. Hopefully that will provide more clues about the problem.

  • #208 Kramer said 2020-05-24T14:14:49Z

    Quick note to anyone out there experiencing this error: "raise SMTPServerDisconnected('please run connect() first') SMTPServerDisconnected: please run connect() first"

    When Miguel says check your email server configuration, make sure you check it for the terminal session you're running the Flask app in. For example, I've been using one terminal window to set environment variables and another to actually run the Flask app. When I was trying to debug this error, I checked the env variables in the window where I was setting them, and they looked fine. But after a few hours of struggling and debugging every part of this I found that the env variables were not set properly in the terminal window that actually contained the running flask app. So you just close the connection, set the env variables, and it works.

    I am a novice developer so I didn't realize this "gotcha" was happening

  • #209 Gitau Harrison said 2020-06-03T23:02:34Z

    @Kramer @miguel

    Thank you for pointing that out, but I still do not get it. I mean, executing flask run on a terminal window and opening the subsequent localhost URL does not fix this the error:

    raise SMTPServerDisconnected('please run connect() first') smtplib.SMTPServerDisconnected: please run connect() first

    All variables are set, the app is running for the very first time

  • #210 Miguel Grinberg said 2020-06-04T09:32:11Z

    @Gitau: I can't really help you because I have no access to your system. I'm pretty sure you are missing some variables, or have set them incorrectly, but you have to debug this yourself to figure out the mistake. Add print statements for all the configuration variables right before the email is sent to check if the variables are what you think they are.

  • #211 Gitau Harrison said 2020-06-06T02:57:42Z

    @Miguel Grinberg

    I have pretty much the same set up of variables as indicated in the blog, painstakingly looking line after line as below:

    SECRET_KEY = os.environ.get('SECRET_KEY') or 'you-will-never-guess' SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or \ 'sqlite:///' + os.path.join(basedir, 'app.db') SQLALCHEMY_TRACK_MODIFICATIONS = False MAIL_SERVER = os.environ.get('MAIL_SERVER') MAIL_PORT = int(os.environ.get('MAIL_PORT') or 25) MAIL_USE_TLS = os.environ.get('MAIL_USE_TLS') is not None MAIL_USERNAME = os.environ.get('MAIL_USERNAME') MAIL_PASSWORD = os.environ.get('MAIL_PASSWORD') ADMINS = ['your-email@example.com']

    Browsing them against your repo, I find them set up correctly. I cannot understand why the server is still disconnected. Every other email feature works extremely well, but getting the app to send that reset email to my inbox is the only hurdle I am struggling with currently.

    For reference, I have my tasks located here (slightly modified for but largely the same) https://github.com/GitauHarrison/somasoma_blog/tree/email_support_feature

  • #212 Miguel Grinberg said 2020-06-06T10:35:06Z

    @Gitau: this just shows the configuration that is imported from environment variables. As I said above, you probably have these variables set incorrectly for your email server.

  • #213 Dip said 2020-06-18T10:48:45Z

    Running through the same problem as Gitau.

    raise SMTPServerDisconnected('please run connect() first') smtplib.SMTPServerDisconnected: please run connect() first

    For everyone else, facing the same problem, try to hard-code the environment variables in the Config file to see if they are working; and if they do, there is one thing you need to know , and this comes from personal experience, that for every terminal session, when you set the mail configurations in the terminal using 'set' or 'export', they live for that terminal session only. The next session, bam, they are gone.

    Use .env file and add it to .gitignore - my Solution.

  • #214 Marv Schier said 2020-07-10T03:40:10Z

    I'm trying to figure out how the password reset works without the db User.token and User.token_expiration ever getting written to or read. I know the password reset works but those db fields are always empty. Are those database fields not even required?

  • #215 Miguel Grinberg said 2020-07-10T08:50:17Z

    @Marv: the password reset token is a JWT. All the information about the user is stored inside the token itself, so for that reason there is no need to store the token in the database.

  • #216 Marv Schier said 2020-07-10T17:25:42Z

    I just noticed your form has the same behavior as mine when the session times out: "The CSRF token has expired." This message is meaningless to most people so I would like to find an easy way to change it and haven't been successful except for an ugly 'hack' in the base template. Any ideas?

  • #217 Miguel Grinberg said 2020-07-11T08:46:58Z

    @Marv: the CSRF token error is hardcoded in the Flask-WTF extension. You can check the form error message and replace it with your own before you pass the form down to the template.

  • #218 Arshit Aggarwal said 2020-07-20T20:53:05Z

    Hi, Thanks for the great series!

    Just a bit curious about the token lifetime. It does expire after 10 mins but ideally it should also expire once the user has changed his password. In the current scenario, I am able to change passwords multiple times with the 10 mins window.

    Kindly share your thoughts on this.


  • #219 Miguel Grinberg said 2020-07-20T22:35:22Z

    @Arshit: JWT tokens expire at the designated time. If you want to deactivate a token after it is used you have to use a different mechanism. In this case you could record the time of the last password change and not allow another change for some length of time.

  • #220 mitchellblom said 2020-07-23T23:40:18Z

    Rather than MAIL_SERVER=smtp.googlemail.com I had to use MAIL_SERVER=smtp.gmail.com

    Thanks so much for this tutorial.

  • #221 injila said 2020-07-25T10:24:46Z

    Hi Miguel, You are doing a great job teaching us all these. I have an error though when working on reset password. smtplib.SMTPServerDisconnected

    smtplib.SMTPServerDisconnected: please run connect() first

  • #222 Miguel Grinberg said 2020-07-25T16:03:36Z

    @injila: your email configuration is incorrect.

  • #223 Vlad said 2020-07-30T01:10:31Z

    Hello Miguel,

    1). Shouldn't there be some kind of a timeout speicified in the mail.send(msg) call? What happens if something's wrong with the mail server and it hangs while connecting? I think we'll potentially run out of memory and the app will crush. I couldn't find any way to set this up for Flask-Mail. 2). Is Flask-Mail a good choice for anything other than a tutorial? It looks unmaintained (last commit was 6 years ago).


  • #224 Md. Tanvir Foysal said 2020-07-30T16:56:21Z

    I've an error in last moment. In browser while I'm trying to reset password. This is given below___:

    raise SMTPServerDisconnected('please run connect() first') smtplib.SMTPServerDisconnected: please run connect() first

    how to fix this??

  • #225 Miguel Grinberg said 2020-07-31T09:24:34Z

    @Vlad: the timeouts are implemented at the socket level, a connection will not hang forever, and you will definitely not run out of memory. You are correct that Flask-Mail isn't currently maintained. Since it is such a simple extension it continues to work, but if that makes you uncomfortable you should just use smtplib from the Python library directly.

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