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.

FolioVision

This plugin reconfigures the wp_mail() function to use SMTP instead of mail() and creates an options page that allows you to specify various options.
You can set the following options:
<ul>
<li>Specify the from name and email address for outgoing email.</li>
<li>Choose to send mail by SMTP or PHP’s mail() function.</li>
<li>Specify an SMTP host (defaults to localhost).</li>
<li>Specify an SMTP port (defaults to 25).</li>
<li>Choose SSL / TLS encryption (not the same as STARTTLS).</li>
<li>Choose to use SMTP authentication or not (defaults to not).</li>
<li>Specify an SMTP username and password.</li>
</ul>
Also adds subject to headers for SendGrid Activity Screen. SengGrid is a powerful SMTP service, however it’s Activity Log screen misses the message subjects. Our plugin adds that back in!

WP Mail SMTP SendGrid Edition

Based on WP Mail SMTP. Also adds subject for display on SendGrid Activity Screen.

Mail Debug vs WP Mail SMTP SendGrid Edition