socketlabs

SocketLabs is a cloud-based email delivery platform built to help you send your marketing and transactional email from one platform. SocketLabs provides optimized email delivery at scale, real-time tracking and analytics, reliable Email APIs for developers, and a suite of Email Marketing Tools that will make sending your next email campaign a breeze.
The SocketLabs WordPress Plugin allows you to easily route email generated by WordPress through SocketLabs rather than the default wp_mail() function that WordPress provides.
Use the SocketLabs plugin if:
<ol>
<li>Your mail from WordPress is failing to be delivered and you need an easy way to get your email to the inbox.</li>
<li>You’re looking for better Inbox placement over an optimized email network.</li>
<li>You would like to get more insight into the performance of your email from our detailed reports in the SocketLabs Control Panel.</li>
<li>Your WordPress instance has been blacklisted and you need to get your mail flowing again.</li>
<li>Your WordPress site is exceeding the number of emails allowed by your ISP.</li>
</ol>
By using the SocketLabs plugin, you can finally take advantage of improved deliverability from WordPress, while benefiting from our powerful delivery platform that’s built to get your emails to the inbox. And in your SocketLabs Control Panel, you’ll be able to take advantage of our expanded feature set, including in-depth tracking and analytics, a Drag and Drop Email Designer, list management, and so much more!
For more details, please visit our official documentation here: 
https://www.socketlabs.com/blog/configure-wordpress-plugin/
<h3>How do I create a SocketLabs account?</h3>
You can sign up for a free account here https://socketlabs.com/signup_form/?plan=Free.
<h3>Help & Support</h3>
Visit our Support System if you have any questions, the SocketLabs Support Team is happy to help — https://support.socketlabs.com/

SocketLabs

The SocketLabs WordPress Plugin allows you to easily send email generated by WordPress through the SocketLabs Email Delivery Service.

Jeff Starr

Enables custom headers for WP email notifications 
Also “set it and forget it” security fix for WP < 5.5
Important
As of WordPress 5.5, this plugin no longer is necessary to fix the <a href="https://exploitbox.io/vuln/WordPress-Exploit-4-7-Unauth-Password-Reset-0day-CVE-2017-8295.html" rel="nofollow ugc">host-header security issue</a> reported in <a href="https://core.trac.wordpress.org/ticket/25239" rel="nofollow ugc">Ticket #25239</a> finally is fixed, and mentioned in this post <a href="https://wordpress.org/news/2020/07/wordpress-5-5-beta-4/" rel="ugc">WordPress 5.5 Beta 4</a>. Thank You WordPress devs!
Is this plugin still useful?
Yes, it enables you to choose the “From”, “Name”, and “Return-Path” headers for all WP notification emails. And for versions of WordPress less than 5.5, this plugin continues to fix the host-header injection security issue.
Features
This simple plugin does three things:
<ol>
<li>Sets custom From, Name, and Return-Path for WP notifications</li>
<li>Fixes a security vulnerability in WordPress versions < 5.5</li>
<li>Fixes a bug where invalid email addresses may be generated (in WordPress versions < 5.5)</li>
</ol>
Choose from the following options:
<ul>
<li>Use WordPress defaults (insecure for WP < 5.5)</li>
<li>Use “Email Address” from WP General Settings</li>
<li>Use a custom name and address</li>
</ul>
Plus there is an option to use the specified From address as the Return-Path header.
Why?
The security issue fixed by this plugin has been known about since way back in WordPress version 2.3. There has been some talk about fixing, but nothing has been implemented. While the issue does not affect all sites, it does affect a good percentage of them, including some of my own projects. So, not wanting to get hacked, I decided to write my own solution. Hopefully this issue gets fixed in a future version of WordPress, and this plugin will become unnecessary.
As a bonus, setting an explicit From address resolves a long-standing bug whereby an invalid email address is generated under the following conditions:
<ul>
<li>A “From” address is not set, </li>
<li>And the <code>$_SERVER['SERVER_NAME']</code> is empty</li>
</ul>
So by explicitly setting a “From” address, we prevent this bug from happening.
Security Issue
What is the security issue addressed by this plugin? Follows is a quick summary. To learn more in-depth, check out the resources linked in the next section.
<ul>
<li>WordPress uses <code>$_SERVER['SERVER_NAME']</code> to set the “From” header in email notifications</li>
<li>This includes sensitive email notifications like password resets and user registration</li>
<li>In some cases, an attacker could modify the “From” header and intercept the email</li>
<li>Using the intercepted email, an attacker could gain access to your site and wreak havoc</li>
</ul>
More Infos
This security vulnerability is well-known and has been around for a looong time. To learn more, check out these articles:
<ul>
<li><a href="https://core.trac.wordpress.org/ticket/25239" rel="nofollow ugc">WP Core Trac Ticket</a></li>
<li><a href="https://wpvulndb.com/vulnerabilities/8807" rel="nofollow ugc">WP Vulnerability Database</a></li>
<li><a href="https://exploitbox.io/vuln/WordPress-Exploit-4-7-Unauth-Password-Reset-0day-CVE-2017-8295.html" rel="nofollow ugc">Exploit Box Info</a></li>
<li><a href="https://blog.dewhurstsecurity.com/2017/05/04/exploitbox-wordpress-security-advisories.html" rel="nofollow ugc">Even more infos</a></li>
</ul>
Privacy
This plugin does not collect or store any user data. It does not set any cookies, and it does not connect to any third-party locations. Thus, this plugin does not affect user privacy in any way.
Host Header Injection Fix is developed and maintained by <a href="https://x.com/perishable" rel="nofollow ugc">Jeff Starr</a>, 15-year <a href="https://plugin-planet.com/" rel="nofollow ugc">WordPress developer</a> and <a href="https://books.perishablepress.com/" rel="nofollow ugc">book author</a>.
Support development
I develop and maintain this free plugin with love for the WordPress community. To show support, you can <a href="https://monzillamedia.com/donate.html" rel="nofollow ugc">make a donation</a> or purchase one of my books:
<ul>
<li><a href="https://wp-tao.com/" rel="nofollow ugc">The Tao of WordPress</a></li>
<li><a href="https://digwp.com/" rel="nofollow ugc">Digging into WordPress</a></li>
<li><a href="https://htaccessbook.com/" rel="nofollow ugc">.htaccess made easy</a></li>
<li><a href="https://wp-tao.com/wordpress-themes-book/" rel="nofollow ugc">WordPress Themes In Depth</a></li>
<li><a href="https://books.perishablepress.com/downloads/wizards-collection-sql-recipes-wordpress/" rel="nofollow ugc">Wizard’s SQL Recipes for WordPress</a></li>
</ul>
And/or purchase one of my premium WordPress plugins:
<ul>
<li><a href="https://plugin-planet.com/bbq-pro/" rel="nofollow ugc">BBQ Pro</a> – Blazing fast WordPress firewall</li>
<li><a href="https://plugin-planet.com/blackhole-pro/" rel="nofollow ugc">Blackhole Pro</a> – Automatically block bad bots</li>
<li><a href="https://plugin-planet.com/banhammer-pro/" rel="nofollow ugc">Banhammer Pro</a> – Monitor traffic and ban the bad guys</li>
<li><a href="https://plugin-planet.com/ga-google-analytics-pro/" rel="nofollow ugc">GA Google Analytics Pro</a> – Connect WordPress to Google Analytics</li>
<li><a href="https://plugin-planet.com/head-meta-pro/" rel="nofollow ugc">Head Meta Pro</a> – Ultimate Meta Tags for WordPress</li>
<li><a href="https://plugin-planet.com/simple-ajax-chat-pro/" rel="nofollow ugc">Simple Ajax Chat Pro</a> – Unlimited chat rooms</li>
<li><a href="https://plugin-planet.com/usp-pro/" rel="nofollow ugc">USP Pro</a> – Unlimited front-end forms</li>
</ul>
Links, tweets and likes also appreciated. Thank you! 🙂

Host Header Injection Fix

Sets custom headers for WP notification emails. Also fixes a security issue with WP versions < 5.5.

SocketLabs vs Host Header Injection Fix