How to troubleshoot emails not sending out
First thing to check when no emails are being sent or you're not getting any emails from your pbx, is to ssh to your pbx and login as root and check /var/log/maillog file
Another thing to check is the email address, say yourname@yourdomain.com, you need to check the MX Entry for yourdomain.com in the dns zone with your registrar, make sure it is setup correctly and correspond to whatever showing up in the above /var/log/maillog
2nd thing to check is make sure your pbx IP is in the whitelist of the email server for yourdomain.com and check the spam filter/folder of yourdomain.com email server to make sure you can receive emails from your PBX IP.