SendGrid: A powerful tool for converting emails into apps

SendGrid is not only a service that sends mail in batches, it also provides a lesser-known powerful feature: processing received mail. With simple configuration, you can let SendGrid process all emails under the specified domain name and send email messages to your server. This article will introduce how to build a "mail to article" function using SendGrid.

Core points:

• SendGrid's inbound mail resolution function can process all messages from a specified domain name and send mail information to the specified URI in the form of a POST request.
• By setting up a webhook, you can customize the received emails.
• SendGrid's inbound email resolution function is widely used, such as: email arrival reminder, attachment upload to cloud storage, email reply forum notifications, processing unsubscribe requests, etc.
• SendGrid's inbound resolution Webhook supports the use of wildcard subdomains to process multiple email addresses, supports HTTPS secure data transmission, the total size of the attachment is limited to 20MB, and provides dashboard activity logs for easy debugging.

Beginner:

The sample code in this article is based on the Slim Framework framework. For easy debugging, please add the following content in the composer.json section: require

"slim/extras": "dev-develop"

Modify the framework instantiation code in

and configure the logger: include/services.php

$app = new Slim(array(
    'view' => new Twig(),
    'templates.path' => $c['config']['path.templates'],
    'log.writer' => new \Slim\Extras\Log\DateTimeFileWriter(array(
        'path' => dirname($c['config']['path.logs']),
        'name_format' => 'Y-m-d',
        'message_format' => '%label% - %date% - %message%'
    ))
));

Copy the sample configuration file to

and set your configuration value (such as database connection information). Add the following code to specify the directory where the log file and upload the image: config/config.php

'path.logs'    => $basedir . 'logs/',
'path.uploads' => $basedir . 'public/uploads/'

Create these directories and make sure the web server has write permissions.

Our app will provide registered users with an email alias. By matching the part before the

symbol in the recipient's email address, we can determine the user who posted it. In practical applications, you may need to set more complex aliases rules and limit email sending addresses. The database structure defines two tables for storing users and articles: @

CREATE TABLE users (
    id INTEGER NOT NULL AUTO_INCREMENT,
    name VARCHAR(128) NOT NULL ,
    alias VARCHAR(45) NOT NULL ,

    PRIMARY KEY (id) ,
   INDEX alias (alias ASC)
);

CREATE  TABLE posts (
    id INTEGER NOT NULL AUTO_INCREMENT,
    title VARCHAR(255) NOT NULL,
    body TEXT NOT NULL,
    image varchar(255),
    user_id INTEGER NOT NULL,

    PRIMARY KEY (id)
);

You need a SendGrid account (free account is sufficient). After registering, go to the developer page and click "Analyze the incoming email". Enter your hostname and callback URL.

When receiving a message with the specified domain name, SendGrid will send a POST request to your URL, including the sender, recipient, email body and attachment information. Finally, you need to add an MX record to your domain name, pointing to

. The specific operation depends on your hosting provider. mx.sendgrid.net

Build callback function:

Your application needs to respond to the POST request of the URL you specified, for example:

"slim/extras": "dev-develop"

If SendGrid's "ping" test returns a 4xx or 5xx error, it queues the request and tries again for 3 days. Therefore, a successful ping test must return a 200 status code. SendGrid's POST request contains various information about the email, please refer to the SendGrid API documentation for details. We mainly focus on the following fields:

Because the to field formats are diverse, we need regular expressions to parse multiple recipients:

$app = new Slim(array(
    'view' => new Twig(),
    'templates.path' => $c['config']['path.templates'],
    'log.writer' => new \Slim\Extras\Log\DateTimeFileWriter(array(
        'path' => dirname($c['config']['path.logs']),
        'name_format' => 'Y-m-d',
        'message_format' => '%label% - %date% - %message%'
    ))
));

For each recipient, extract the alias section and find the matching user:

'path.logs'    => $basedir . 'logs/',
'path.uploads' => $basedir . 'public/uploads/'

Create an article:

CREATE TABLE users (
    id INTEGER NOT NULL AUTO_INCREMENT,
    name VARCHAR(128) NOT NULL ,
    alias VARCHAR(45) NOT NULL ,

    PRIMARY KEY (id) ,
   INDEX alias (alias ASC)
);

CREATE  TABLE posts (
    id INTEGER NOT NULL AUTO_INCREMENT,
    title VARCHAR(255) NOT NULL,
    body TEXT NOT NULL,
    image varchar(255),
    user_id INTEGER NOT NULL,

    PRIMARY KEY (id)
);

Now we have the basic "email to article" function! Next, we can add attachment processing function, allowing users to add images through email attachments. SendGrid's POST request contains the attachments parameter, indicating the number of attachments. Attachments are POSTed together with requests, and the processing method is the same as that of uploading web form files.

$app->post('/endpoints/email', function () use ($app, $c) {

Summary:

This article introduces a simple application of SendGrid's inbound email resolution function - the "Mail to Article" function, which allows users to create articles by sending emails. Through simple callback functions, you can implement various interesting functions, such as: email arrival reminder, attachment upload to cloud storage, email reply forum notifications, processing unsubscribe requests, etc.

(The subsequent content, namely the FAQ part, is recommended to deal with it separately due to the length of the article. The FAQ part can be submitted separately as a new question.)

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