After migrating from WP my existing SMTP plugin (WP Mail SMTP) was working but caused a site error when going to settings. So I have installed a CP SMTP plugin by Azurecurve. This gives an error when sending a test email:
I can’t offer any technical advice, but have had no problem with the plugin. Although I “think” my first test email on my last site may have given that error message - but it was delivered.
I just use: mail.mysite.com
cPanel username
cPanel password
website email address
I also set the from address and from name. Everything else I leave untouched.