Proxmox Notification Email Error

Proxmox is using postfix as email software, and the configuration of sender email uses local hostname+domain name as below in /etc/postfix/main.cf

myhostname=full qualified hostname

Issue

The postfix tries to look for email receiver's email server, and send emails directly to the email server using myhostname defined in /etc/postfix/main.cf as senders DNS name. But the server hostname normally isn't using the public valid domain name, which causes email server rejects notification emails.

Fix

Change the default myhostname in /etc/postfix/main.cf to a valid public email domain name.