To combat spam, virtually all hosting providers have implemented new rules pertaining to the sending and delivery of emails. Most Internet Service Providers totally block downstream servers from sending email at all. Because the required settings for email servers are server-specific even on servers directly connected to the Internet, your safest bet for delivery of outbound emails from your server is to configure a smarthost relay such as Gmail which handles all the intricacies of email delivery for you.
On most Incredible PBX platforms, there is a script in the /root folder to configure a Gmail Smarthost. The script name begins with enable-gmail-smarthost. You will need the Google credentials for your Gmail account to complete the procedure. Be advised Google is phasing out so-called “Less Secure Apps” so you must use a Google App Password as your Gmail password.
In the alternative, you may prefer to use a non-Gmail email account for your Smarthost relay. This Nerd Vittles article will walk you through the process.