Hi there,
As part of our work refactoring and expanding email sending options in v8.0, an email connection tester has been added when modifying email provider settings.
This is located under Configuration > System Settings > General Settings > Mail tab > Configure Mail Provider.

Beta information: https://beta.whmcs.com

Feature documentation: https://docs.whmcs.com/Mail_Providers

Feature spotlight: https://blog.whmcs.com/133638/feature-spotlight-email-delivery-providers

Discussion: https://whmcs.community/topic/301821-email-delivery-providers-share-your-experience/