There was a problem while sending a test email.

The related debugging output is shown below:

Versions

WordPress: 4.9.1
PHP: 5.6.32
WP Mail SMTP: 1.0.2

PHPMailer

ErrorInfo: SMTP connect() failed.  https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
Mailer: smtp
Host: smtp.zoho.com
Port: 465
SMTPSecure:  ssl
SMTPAutoTLS:  bool(true) 
SMTPAuth:  bool(true)

SMTP Debug

2017-12-15 22:10:40 SMTP ERROR: Failed to connect to server: Connection refused (111)
2017-12-15 22:10:40 SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting