First make sure you have enabled logging under Email Settings, and you can either log in to the server and pull the file from /usr/local/nagiosxi/tmp/phpmailer.log, or send us your system profile. Thanks.Test message worked just fine. What the easiest way to get you that file. I'm not sure how to get it.
To send us your system profile.
Login to the Nagios XI GUI using a web browser.
Click the "Admin" > "System Profile" Menu
Click the "Download Profile" button
Save the profile.zip file and share in a private message and then reply to this post to bring it up in the queue.