Acato

Email Essentials vastly reduces the chances of your emails being marked as spam or being rejected. Originally a debugging tool, it has grown into a full-fledged email enhancement plugin.
Please note that this plugin is not a “we support any type of transport” Email plugin. For other protocols than SMTP, but rather to enhance the email sending capabilities of WordPress. 
If you need to send emails with other protocols than SMTP, this plugin is not for you. You might want to look at plugins like Post SMTP (not affiliated).
And since version 6.0.0, after more than 10 years of development, this plugin is now a FOSS plugin, meaning it is free to use, modify and distribute under the GPLv2 license.
In return, we ask you to support the development of this plugin by contributing to the codebase, reporting bugs, and helping others in the community.
Responsible disclosure: 
If you find a vulnerability, please email us at <a href="mailto:responsibledisclosure@acato.nl" rel="nofollow ugc">responsibledisclosure@acato.nl</a>.
<h3>Features</h3>
<ul>
<li>Set a good From name and email address, automatically correcting it if needed. For example, a contact form is sent from the visitors email address, resulting in an invalid Sender address. This plugin will correct it to a valid email address. This plugin automatically corrects it.</li>
<li>Correct envelope-from address; often forgotten, but important for deliverability.</li>
<li>Reformat as HTML with plain text alternative; will detect the use of HTML ensures that emails are sent as HTML with a plain text alternative.</li>
<li>Process shortcodes in your email content.</li>
<li>UTF8 recoding, to ensure that special characters are correctly encoded in the email.</li>
<li>Email Essentials allows for adding CSS, header, footer, and body template using filters, see below.</li>
<li>Convert CSS to inline styles for better support in email clients</li>
<li>SMTP configuration</li>
<li>Send emails to multiple addressees as separate emails</li>
<li>S/MIME signing, using a supplied certificate, to ensure the authenticity of the email.</li>
<li>DKIM signing, and providing all information needed to set up DKIM signing for your domain.</li>
<li>Allow redirecting emails sent to the administrator to other email addresses based on the email subject.</li>
<li>Allow redirecting emails sent to the moderators (e.g., for comments).</li>
<li>Keep a history of outgoing emails (debugging, cleared on deactivation)</li>
<li>Email receipt tracking (for investigative purposes only, see GDPR note)</li>
<li>Re-send button for failed emails</li>
<li>Allow sending emails delayed, to prevent sending too many emails at once. (Beta feature)</li>
</ul>
<h3>Important Note</h3>
This tool is for users who understand email delivery. If unsure, ask for help.
Under GDPR, storing and tracking emails is prohibited. The history feature is for investigative purposes only!
<h3>External services</h3>
Email Essentials uses one external service by default, two if you create and define your own IP services.
<ol>
<li>CloudFlare DNS over HTTPS (DoH). This is used to resolve domain names to IP addresses when (for example) checking SPF or DKIM records. In theory, it is possible to use PHPs own <code>dns_get_record</code> function, but in practice this often fails due to server DNS-resolve misconfiguration. Using CloudFlare’s DoH service ensures reliable DNS resolution. We only send the hostname (the domain part) to CloudFlare, no other data. Explicitly, we do NOT send any other information.</li>
<li>The plugin can use an IP-address relay service to accurately determine the sender’s IP address. This is required to accurately check that the sender’s IP address is authorized to send email for the domain (SPF check). To use this, you will need to set up your own service, see documentation on filter <code>acato_email_essentials_ip_services</code>. Without this service, IP detection can be inaccurate because it will use the website itself as a relay. Use of a reverse proxy, load balancer etc. can lead to incorrect IP detection.</li>
</ol>
<h3>WordPress Filters</h3>
<ul>
<li><code>acato_email_essentials_settings</code> — Filter plugin settings.</li>
<li><code>acato_email_essentials_defaults</code> — Filter default settings.</li>
<li><code>acato_email_essentials_subject</code> — Filter email subject.</li>
<li><code>acato_email_essentials_body</code> — Filter HTML body of the email.</li>
<li><code>acato_email_essentials_head</code> — Filter HEAD section of HTML email.</li>
<li><code>acato_email_essentials_css</code> — Filter CSS for the email.</li>
<li><code>acato_email_essentials_minify_css</code> — Filter CSS minification.</li>
<li><code>acato_email_essentials_mail_is_throttled</code> — Check if mail should be throttled.</li>
<li><code>acato_email_essentials_mail_throttle_time_window</code> — Set mail throttle time window.</li>
<li><code>acato_email_essentials_mail_throttle_max_count_per_time_window</code> — Set max emails per time window.</li>
<li><code>acato_email_essentials_mail_throttle_batch_size</code> — Set mail batch size.</li>
<li><code>acato_email_essentials_ip_services</code> — Define custom IP services for accurately determining the sender’s IP address.</li>
<li><code>acato_email_essentials_ip_service</code> — Filter individual IP service URLs.</li>
<li><code>acato_email_essentials_website_root_path</code> — Filter to supply the correct website root path in case of non-standard setups.</li>
<li><code>acato_email_essentials_development_tlds</code> — Filter development/local TLDs.</li>
</ul>
<h3>WordPress Filters in detail</h3>
Plugin Settings
<pre><code>acato_email_essentials_settings
</code></pre>
Parameters: 
– (array) <code>$settings</code> The current settings of the plugin.
Expected return: 
– (array) The new settings of the plugin.
<pre><code>acato_email_essentials_defaults
</code></pre>
Parameters: 
– (array) <code>$defaults</code> The current default settings of the plugin.
Expected return: 
– (array) The new default settings of the plugin.
Email Content
<pre><code>acato_email_essentials_subject
</code></pre>
Parameters: 
– (string) <code>$the_subject</code> Subject for the email. 
– (PHPMailer) <code>$mailer</code> The PHPMailer object (by reference).
Expected return: 
– (string) The (altered) Subject.
<pre><code>acato_email_essentials_body
</code></pre>
Parameters: 
– (string) <code>$should_be_html</code> A text that should be html, but might not yet be, your job to make a nice HTML body. 
– (PHPMailer) <code>$mailer</code> The PHPMailer object (by reference).
Expected return: 
– (string) A text that should be html.
<pre><code>acato_email_essentials_head
</code></pre>
Parameters: 
– (string) <code>$the_head_section</code> HTML that is the HEAD section of the HTML email. 
– (PHPMailer) <code>$mailer</code> The PHPMailer object (by reference).
Expected return: 
– (string) The altered HEAD section of the HTML email.
<pre><code>acato_email_essentials_css
</code></pre>
Parameters: 
– (string) <code>$the_css</code> CSS for the email (empty by default). 
– (PHPMailer) <code>$mailer</code> The PHPMailer object (by reference).
Expected return: 
– (string) The (altered) CSS.
<pre><code>acato_email_essentials_minify_css
</code></pre>
Parameters: 
– (string) <code>$css</code> CSS to be minified.
Expected return: 
– (string) The minified CSS.
Mail Throttling
<pre><code>acato_email_essentials_mail_is_throttled
</code></pre>
Parameters: 
– (bool) <code>$is_throttled</code> Whether the mail is currently throttled. 
– (string) <code>$ip</code> The sender’s IP address. 
– (int) <code>$mails_recently_sent</code> Number of mails recently sent from this IP.
Expected return: 
– (bool) Whether the mail should be throttled.
<pre><code>acato_email_essentials_mail_throttle_time_window
</code></pre>
Parameters: 
– (int) <code>$time_window</code> Time window in seconds for counting sent emails.
Expected return: 
– (int) The (altered) time window in seconds.
<pre><code>acato_email_essentials_mail_throttle_max_count_per_time_window
</code></pre>
Parameters: 
– (int) <code>$count</code> Maximum number of emails allowed per time window.
Expected return: 
– (int) The (altered) maximum count.
<pre><code>acato_email_essentials_mail_throttle_batch_size
</code></pre>
Parameters: 
– (int) <code>$size</code> Number of emails to send in a single batch.
Expected return: 
– (int) The (altered) batch size.
IP Detection
<pre><code>acato_email_essentials_ip_services
</code></pre>
Parameters: 
– (array) <code>$services</code> The current list of IP services used to determine the sender’s IP address.
Expected return: 
– (array) The (altered) list of IP services.
The services must be keyed with <code>ipv4</code>, <code>ipv6</code> and <code>dual-stack</code>. The values must be URLs that return the IP address in plain text. 
The dual-stack service should return an IPv6 address if available, otherwise an IPv4 address, never both.
You can set-up your own service like this;
<ul>
<li>You will need a webserver that can run PHP, and you need a DNS service that allows you to manually add records.</li>
<li>You will need three webspaces, for example; ipv4.myservice.com, ipv6.myservice.com and dual-stack.myservice.com.
<ul>
<li>You could use the same webspace for all three, but you will still need three subdomains on the service.</li>
</ul>
</li>
<li>For the ipv4 subdomain, ONLY register an A record, pointing to the webserver’s IP address.</li>
<li>For the ipv6 subdomain, ONLY register an AAAA record, pointing to the webserver’s IPv6 address.</li>
<li>For the dual-stack subdomain, register both an A and an AAAA record, pointing to the webserver’s IP addresses.</li>
<li>
Create a file called <code>index.php</code> in each of the webspaces with the following content:
<code>php 
<?php 
header('Content-Type: text/plain'); 
print $_SERVER['REMOTE_ADDR'];</code>
</li>
</ul>
That’s it. You can now use these services in the plugin settings like this;
<pre><code>`php
</code></pre>
add_filter(‘acato_email_essentials_ip_services’, ‘my_custom_ip_services’); 
function my_custom_ip_services($services) { 
 // Add your custom services here 
 $services[‘ipv4’] = ‘https://ipv4.myservice.com’; 
 $services[‘ipv6’] = ‘https://ipv6.myservice.com’; 
 $services[‘dual-stack’] = ‘https://dual-stack.myservice.com’; 
 return $services; 
} 
 `
<pre><code>acato_email_essentials_ip_service
</code></pre>
Parameters: 
– (string) <code>$service</code> The URL of the IP service for the given type. 
– (string) <code>$type</code> The type of IP service (‘ipv4’, ‘ipv6’, or ‘dual-stack’).
Expected return: 
– (string) The (altered) IP service URL.
Filter to modify individual IP service URLs based on type.
<pre><code>acato_email_essentials_website_root_path
</code></pre>
Parameters: 
– (string) <code>$path</code> The current website root path.
Expected return: 
– (string) The (possibly altered) website root path.
Filter to supply the correct website root path in case of non-standard setups.
<pre><code>acato_email_essentials_development_tlds
</code></pre>
Parameters: 
– (array) <code>$tlds</code> Array of top-level domains considered as development environments.
Expected return: 
– (array) The (altered) array of development TLDs.
Filter to modify which TLDs are treated as development/local environments. Default values are ‘local’ and ‘test’.
<h3>Scripts/styles</h3>
In the <code>public/scripts</code> and <code>public/styles</code> folder you find the JS and CSS files used in the plugin admin area. 
These files are processed with Webpack, just so it works in all recent browsers. Script is nearly identical to the source.
You can find the source files in the <code>src/scripts</code> and <code>src/styles</code> folders.
If you feel the need to modify these files, you can change them there, and run <code>npm install ; npm run build</code> to create the production files.
<h3>Translation files</h3>
You can use <code>npm run i18n</code> to generate the POT file for translation, update the PO files in the <code>languages</code> folder, and compile to MO/php files. 
This is a one-task-does-all; run it, change the translations, run it again. Done. 
See package.json for more details or individual commands.
<h3>Tools</h3>
In the <code>tools</code> folder you will find a script to generate DKIM keys, should you want to use DKIM signing. 
rename to remove the .txt extension and run it in a shell.
Tools are provided as-is, without support. Use at your own risk. Read the scripts before using them.
You DO NOT HAVE TO USE these scripts, you can generate DKIM keys with any tool you like.
<h3>Arbitrary section</h3>
For advanced configuration and custom IP services, see the plugin documentation or source code.

Email Essentials

A plugin to make WordPress outgoing emails better and less likely to be marked as spam.

Liups233

This plugin is for signing all outbound emails with an S/MIME certificate.
It uses phpmailer to automatically sign emails. Here are the prerequisites to use this plugin: 
* This plugin is for single-user WordPress site, such as a personal blog. I don’t know what will happen if you put it in a multi-user site. 
* PHP 8.3 and above are recommended. Make sure your PHP has openssl extension, which is usually installed by default. 
* You should use another plugin, such as FluentSMTP, to send emails through an external SMTP server.

S/MIME Email Signing

A plugin for signing all outbound emails with an S/MIME certificate.

Email Essentials vs S/MIME Email Signing