We have switched to PHP 7. We have been getting the error below when an order placed at customer side:
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting.
What is the problem and solution?
I switched to the "via php mail function" option under Settings > E-mails.
Verify the hostname of your SMTP server. I think you'd get a different error if you had an authentication failure but not entirely sure.