Steps to reproduce the issue

Enter SMTP settings into the Global Config page, Server tab.
Click 'Send Test Mail'

Expected result

Receive a test email.

Actual result

Nothing. The screen did not respond to the Test Email button.
Debugging ON, no info there either.

System information (as much as possible)

PHP Built On Linux sh34-554.ich-5.com 2.6.32-042stab116.2 #1 SMP Fri Jun 24 15:33:57 MSK 2016 x86_64
Database Type mysql
Database Version 5.6.41
Database Collation latin1_swedish_ci
Database Connection Collation utf8_general_ci
PHP Version 7.2.12
Web Server Apache
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 4.0.0-alpha5 Alpha [ Amani ] 4-November-2018 23:23 GMT
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36

Additional comments

SMTP Settings exactly the same as in Joomla 3.9 on same server.