SMTP.com

<a href="https://smtp.com" rel="nofollow ugc">SMTP.com</a> was the first company to provide email delivery at scale for customers unsatisfied with traditional sending methods. With over 22 years of email delivery success, SMTP.com is the trusted transactional and email relay provider for over 100,000 businesses worldwide. This WordPress integration for SMTP.com enables you to send and track your emails seamlessly.
Don’t worry about maintaining your email server or taking care of its IP reputation, forget about dealing with ISPs like Gmail, Yahoo or Microsoft in attempting to understand why your email isn’t reaching its destination. SMTP.com manages all this on your behalf. Simply create a SMTP.com account to <a href="https://registration.smtp.com/?afid=wpplugin" rel="nofollow ugc">get started</a> and set up this plugin. Although this plugin is free you will need a paid subscription with SMTP.com to send emails from your WordPress site.
You can send emails from your WordPress site using the SMTP.com API or the standard SMTP protocol. Our plugin will suggest the best way for you to send email even if your provider has restricted access to outbound internet ports. Either way, SMTP.com will still ensure your email gets delivered.
Another useful feature provided with our WordPress plugin is the ability to track your email delivery from within the plugin itself. See the results of your recent sends to ensure successful delivery or identify the reason why your particular email hasn’t been delivered.


Didn't work with the API key, but managed with the login information.


Good

SMTP.com is a powerful and reliable SMTP delivery service that enables you to send and track high volume emails effortlessly.

WonderPlugin

Display wp_mail Error Messages
Many plugins use the WordPress function <a href="https://developer.wordpress.org/reference/functions/wp_mail/" rel="nofollow ugc">wp_mail</a> to send emails. When an error happens, it’s hard to locate the problem. This plugin will catch the wp_mail error messages and display them.
Features
<ul>
<li>Easy to use</li>
<li>Automatically clear the log when it exceeds the defined maximum length limit.</li>
</ul>
How to Use
After the plugin is installed and activated, in the WordPress backend, goto the left menu WP Error Messages -> Show Errors.

Display wp_mail Error Messages

I just found this plugin and it has been very helpful with debugging. Thank you for this!

SMTP.com vs Display wp_mail Error Messages