Hi, Sendmail should already be running and no need to change the configuration on it.
You need to do the following:
1. Wirte down the email address you are trying to send the email notifiation to. i.e. firstname.lastname@example.org
2. Open your console not asterisk CLI, but Linux CLI. Then run the following command:
Make sure that the IP address that it returns is in deed the correct IP address for that mail server.
3. If this is not correct you aree more than likely usgin your internal DNS servers to resolve the domain name it will tryto route all your emails to your local server instead of your exten mail server (if you have one). You need to go into /etc/resolv.conf and change the IP address for the name server in there to your ISP instead of internal DNS server.
4. Restart and test.
5. If this does not work then you need to go into your /etc/hosts file and add your DNS domain in there: pbx.abc.com
Let me know if this helps