We have a DHVC form in our WP website for our clients to schedule a demo. The form records data correctly but not sending email. We have tested with other plugins and they can send email with the same SMTP settings. Do you have any ideas why this happens?

The SMTP settings are

Host: our email server

Port: 25

Encryption: None

We have checked our email server logs and found the connection between the form, WP site IP address, and our email server but somehow the connection failed with TLS attempts as the last line we saw in the logs.

Configuration

IIS 10.0.14393.0

PHP 7.3.7

Wordpress 5.3

WPBakery: 6.0.5

DHVC Form: 2.2.34

Anything that we missed?