This plugin when activated automatically redirects all email sent through wp_mail/phpmailer to the user currently logged in or the site administrator.
The redirected email contains information about where the original email would have been sent to.
Use this plugin if you want to test email-sending features without actually sending emails our to anyone but yourself. I wrote this plugin to ease debugging with subscribe2.
Since Version 1.2 you can choose whether to redirect all email to the currently logged in user (default), the site administrator (only wpmu) or the blog administrator.

Mail Debug

Redirects all email sent through wordpress to the user currently logged in or the site administrator.

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!

Mail Debug vs Display wp_mail Error Messages